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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A white powder is used by doctors to support fractured bones. (a) Write the name and chemical formula fo the powder. (b) How is this powder (c) When this white powder is mixed with water, a hard solid mass is obtained. Write a balanced chemical equations for the changes. (d) Give one more use of this white powder. |
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Answer» (a) Name of white powder. Calcium sulphate hemi-hydrate. Chemical formula - `CaSO_(4) .1//2H_(2)O` . (b) It is prepared by heating gypsum at 373 K. `underset("Gypsum")(CaSO_(4).2H_(2)O) overset(373K)tounderset("plaster of Paris")(CaSO_(4).""^(1//)2H_(2)O+1^(1//2)H_(2)O)` (c) `CaSO_(4).""^(1//2)H_(2)O + 1^(1//2)H_(2)O tounderset("Gypsum")(CaSO_(4).2H_(2)O)` (d) It is the used for making surface smooth. |
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| 2. |
When potassium iodide solution is added to a solution of lead (II) nitrate in a test tube, a precipitate is formed. (a) What is the colour of this precipitate? Name the compound precipitated. (b) Write the balanced chemical equation for this rection. (c) List two types of reactions in which this reaction can be placed. |
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Answer» (a) The precipitate is yellow in colur. It is lead iodide `(PbI_(2))`. (b) `Pb(NO_(3))_(2)(aq)+2Kl(aq)rarrPbI_(2)darr+2KNO_(3) (aq)` (c ) (i) Double Displacement Reaction, (ii) Precipitation Reaction. |
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| 3. |
What happens when 5% alkaline potassium permanganate solution is added drop by drop to warm propyl alcohol (propanol) taken in a test tube? Explain with the help of a chemical equation. |
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Answer» During this reaction the alcohols are converted into carboxylic acids as carbon compounds can be easily oxidised. Therefore, when propanol is heated with alkaline potassium permanganate solution, it gets oxidised to propanoic acid. The colour of the potassium permanganate does not disappear as it is used to oxidise alcohol to acids. `CH_(3)-CH_(2)-CH_(2)OH overset("Alkaline" KMNO_(4))rarrunderset("propanoic acid")(C_(2)H_(5)COOH)` |
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| 4. |
Distinguish between esterification and saponification reactions of organic compounds with the help of the chemical equation for each. Write one use of (i) esters and (ii) saponification process? |
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Answer» Esterification. In such a reaction an alcohol reacts with a carboxylic acid in the presence of conc. `H_(2)SO_(4)` to form sweet smelling compounds called esters. `CH_(3)COOH+C_(2)H_(5)OH underset("Warm")overset(Conc. H_(2)SO_(4))(to) underset("Ethyl ethanoate (ester)")(CH_(3)COOC_(2)H_(5))+H_(2)O` Saponification. In such a reaction an ester reacts with sodium hydroxide to form sodium salt of an acid and alcohol. `CH_(3)COOC_(2)H_(5)+NaOH overset(" Heat ")(to)C_(2)H_(5)OH+underset("Sodium ethanoate")(CH_(3)COONa)` It is a sponification reaction. (i) Esters are used for making of puddings and icecreams, etc. (ii) Saponification process is used in making of various types of soaps. |
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| 5. |
Name one plant hormone which inhibits growth. Write its one more function. |
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Answer» Abscisic acid is a plant hormone which functions mainly as a growth inhibitor. It promotes the dormancy in seeds and buds. It promotes the closing of stamata. It promotes the wilting and falling of leaves. |
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| 6. |
(a) Define reflex action. State its significance. (b) How do plants respond to external stimuli ? |
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Answer» (a) A reflex action is an automatic response to a stimulus. The simplest form of response in the nervous system is reflex action. This is a rapid, automatic response to a stimulus which is not under the voluntary control of brain. It is described as an involuntary action. The pathway taken by nerve impulses in a reflex action is called the reflex arc. Reflex actions are the actions which we perform without thinking to protect ourselves. For example, coughing is a reflex action which clears our windpipe. The pupils of our eyes get smaller in bright light. This reflex action protects the retina of our eyes from damage due to much light. The pupils of our eyes get bigger in dim light so as to help us see properly even in dim light. (b) Plants respond to external stimuli such as light, touch, etc. A growth movement of a plant part in response to an external stimulus in which the direction of stimuli determines the direction of response in called tropism. If the growth of a plant part is towards the stimuli, it is called positive tropism. If the growth of a plant part is away from the stimulus, then it is called negative tropism. Types of tropism: The movement of a plant part in response to light is called phototropism. The movement of a plant part in response to gravity is called geotropism. The movement of a plant part in response to chemicals is called chemotropism. The movement of a plant part in response to water is called hydrotropism. The directional growth movement of a plant part in response to the touch of an object is called thigmotropism. Nasties (or Nastic Movements). The movement of a plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is called nastic movement. The folding up of a the leaves of a sensitive plant on touching is an example of nastic movement. Here the stimulus is touch. The opening up of the petals of dandelion flowers in morning in bright light and closing in the evening when the light fades is an example of nastic movement. In this case the stimulus is light. |
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| 7. |
The rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Give reason. State the pathway of air form nostrials to the lungs in human beings. or Mention three characterisitc features of hormonal secretions in human beings. |
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Answer» The animals which live in water ( aquatic animals) use the oxygen dissolved in water to carry out respiration . Since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore, the rate of breathing in aquatic animals is much faster than in terrestrial animals. A faster rate of breathing provides more oxygen to aquatic animals. Pathway of air in human beings `:` Nostrials `rarr` Pharynx` rarr` Larynx ` rarr` Trachea ` rarr ` Lungs or (i) A group of endocrine glands which produces various hormones is called an endocrine system. The endocrine system is also called hormonal system. (ii) The endocrine system also helps in coordinating the activities of our body . The endocrine system in our body consists of a number of glands ( or tissues ) which make, store, and release chemicals called hormones. (iii) The working of endocrine glands is controlled by our nervous system. The hormones produced by endocrine glands act as messengers between the nervous system and the organs of our body. |
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| 8. |
(a) In electrolysis of water, why is the volume of gas collected over one electrode double that gas collected over the other electrode ? (b) (i) What is observed whern a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube ? (ii) What type of reaction is this ? (iii) Write a balanced chemical equation to represent the above reaction. |
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Answer» (a) In electrolysis of water `(H_(2)O)`, the hydrogen goes to one test tube and oxygen goes to to another. The two electrodes collect H and O separately. Since water `(H_(2)O)` consists of 2 parts of hydrogen and 1 part of oxygen, so, the volume of hydrogen gas `(H_(2))` collected over cathode (negative electrode) is double the volume of oxygen gas `(O_(2))` collected over anode (positive electrode). (b) (i) When potassium iodide solution is added to lead nitrate solution, then a yellow precipitate of lead iodide is produced along with potassium nitrate solution. (ii) This is a double displacement reaction. (iii) `underset("Lead nitrate")(Pb(NO_(3))_(2)(aq))+underset("Potassium iodide")(2KI(aq)) rarr underset("Lead iodide (yellow ppt)")(PbI_(2)(s)) + 2KNO_(3)(aq)` |
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| 9. |
List two observation you would record in your notebook 30 minutes after adding iron filling to copper sulphate solution. |
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Answer» Observation recorded: .Brown coating on the surface of the iron nail. .Blue colour of the copper sulphate solution fades away. |
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| 10. |
You are provided with a container made up of aluminium. You are also provided with solutions of dil HCl, dil `HNO_(3), ZnCl_(2)` and `H_(2)O`. Out of these solutions which solution, can bekept in the aluminium container ? Name the type of reaction taking place. |
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Answer» (i) Dilute HCl cannot be kept in aluminium container because aluminium metal reacts rapidly with dil HCl to form aluminium chloride and liberating hydrogen gas. `2Al(s) +6HCl(dil) rarrunderset("(Displacement reaction)")(2AlCl_(3)(aq))+3H_(2)(g)` (ii) When dilute `HNO_(3)` is kept in aluminium container, it forms a protective layer of aluminium oxide on it which makes it passive towards action with acid and therefore, it can be kept in Aluminium container. `2Al(s)+6NO_(3) rarr underset("(Displacement reaction)")(Al_(2)O_(3))+6NO_(2)+3H_(2)O` (iii) `ZnCl_(2)` solution also cannot be kept in aluminium container because Al is more reactive then Zn, therefore more reactive Al displaces less reactive Zn from its solution `( ZnCl_(2))` . `2Al(s)+3ZnCl_(2)(aq) rarr underset("(Displacement reaction )")(2AlCl_(3))+3Zn` (iv) Aluminium does not react with `H_(2)O` . So, can be kept in aluminium container. |
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| 11. |
Give reason for the following`:` (a) Sodium metal is kept immersed in kerosene. (b) Blue colour of copper sulphate disappers when a some aluminium powder is added in it. |
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Answer» (a) Sodium metal is so reactive that it reacts vigorously with the oxygen ( of air). It catches fire and starts burning when kept open in the air. Sodium metal is stored under kerosene oil to prevent its reaction with oxygen, moisture and carbon dioxide of air. (b) When aluminium powder is put in copper sulphate solution, then the blue colour of copper sulphate solution fades gradully due to the formation of colourless aluminium sulphate solution. `underset("Blue")(3CuSO_(4)(aq))+2Al(s) overset("Displacement")(rarr) underset("Colourless")(Al_(2)(SO_(4))_(3)(aq))+3Cu(s)` Since Al is more reactive than Cu, it displaces Cu from `CuSO_(4)` solution and forms colourless `Al_(2)(SO_(4))_(3)` |
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| 12. |
Which important properties of aluminium are responsible for its great demand in industy? |
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Answer» Important properties of aluminium : (i) It is a light metal . (ii)It does not corrode as it forms a protectiv layer of oxide which prevents it from further oxidation. (iii) It is a good conductor of heat and electricity. (iv) It is used as a reducing agent in the extraction of metals from the oxide. |
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| 13. |
Illustrate any three chemical properties of acids. With examples. |
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Answer» Chenical properties of acid : (i) Acids react with metals to form `H_(2)` gas. ` Zn + 2HCl to Zn Cl_(2) + H_(2) uarr ` (ii) Acids turn blue litmus into red. (iii) Acids react with bases to form salt and water (neutralization reaction ) ` underset ("Acid")(HCl) + underset ("Base")(NaOH) to underset ("Salt")(NaCl) + underset ("Water")(H_(2)O)` |
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| 14. |
Write the number of covalent bonds in the molecular of ethane. |
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Answer» Ethane - `C_(2) H_(6)` `H- underset(H)underset(|)overset(H) overset(|)C-underset(H)underset(|)overset(H) overset(|)C-H` No, of covalent bonds in ethene is7. |
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| 15. |
What are magnetic field lines? List two characteristic properties of these lines. |
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Answer» Magnetic field lines are the lines drawn in a magnetic field along which north magnetic pole would move. The direction of a magnetic field at a point is determined with the help of a small magnetic compass. When a compass is moved along the magnetic line, then direction of called pulvini present at the base of all leaves. |
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| 16. |
Explaing why carbon forms compounds mainly by covalent bond. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements ? |
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Answer» The atomic number of carbon is 6 which means that a neutral atom of carbon, retains 6 electrons. So the electrons configuration of carbon is K=2, L=4. Since, carbon has 4 electrons in tis outmost shell so, it should either lose or gain 4 electrons to achieve the inert gas configuration and becomes table. (i) It could gain four electrons forming `C^(4-)` anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons due to inter electronic repulsion. (ii) It could lose 4 electrons formign `C^(4+)` cation. But it would require a large amount of energy to remove four electrons from its outermost shell. Thus, it forms compounds mainly by covalent bonds. Two properties of carbon which lead to huge number of carbon compounds are `:` (i) Catenation `:` Catenation is the unique property of carbon atoms to form bonds with other atoms of carbon giving rise to large molecules. (ii) Tetravelency `:` Since carbon has a valency of 4, it is capable of bonding with 4 other atoms of carbon or atoms of some other monovalent element. The reason for the formation of strong bonds by the carbon atoms is their small atomic size. Due to the small size of carbon atoms their nuclei hold the shared pairs of electrons between atoms strongly covalent bonds with the atoms of other elements such as hydrogen oxygen, nitrogen , sulphur, chlorine and other elements. |
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| 17. |
(a) Define a universal indicated . Mention its one use. (b) Solution A gives pink colour when a drop of phenolphthalein indicator is added to it. Solution B gives red colour when a drop of methyl orange is added to it. What type of solutions are A and B which one of the solutions A and B will have a higher pH value ? (c) Name one salt whose solutions has pH more than 7 and one salt whose solution has pH less than 7. |
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Answer» (a) Universal indicator is a mixture of many different indicators which gives different colours at different pH values of the entire pH scale. It shows different colours at different concentrations of hydrogen ions in a solution. (b) Solution A gives pink colour when a drop of phenolphthalein indicator is added, therefore A is a base. Solution B gives red colour when a drop of methyl orange is added to it, therefore B is an acid. Hence, solution A will have less concentration of hydrogen ion than B. Thus, A will have pH more than 7 because pH value of : -an acid solution `lt 7` , -a base solution `gt 7` , and - a neutral solution =7 (c) - The salts of strong acids and weak bases give acidic solution have pH less than 7. Example, `NH_(4)Cl`, Ammonium Chloride will have pH less than 7. -The salts of a weak , acids and strong bases give basic solution having pH more than 7. Examples, `Na_(2)CO_(3)`, Sodium Carbonate will have pH more than 7. |
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| 18. |
(a) Write three main functions of the nervous system. (b) In the absence of muscle cells, how do plant cells show movement ? |
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Answer» (a) Main functions of the nervous system `:` Coordinate the activities of the body Helps all other systems of the body to work together. The nervous system receives information fromt eh surroundings, processes it, interprets it and then responds accordingly. (b) The movement in any part of a plant is usually a growth movement or change in shape of body parts. - The movements of the plant part are usually caused by an unequal growth in its two regions by the action of plant hormones, under the influence of the stimuli like light, force of gravity, chemical substences, water touch etc. `-` The change in shape occurs by changing the amount of water in the body part. Water causes swelling and shrinking which causes movement. |
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| 19. |
Name the two components of peripheral nervous system. |
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Answer» Two components of peripheral nervous system `:` Autonomic nervous system. Voluntary nervous system. |
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| 20. |
Write one function each of the following enzymes: (i) Pepsin (ii) Lipase . |
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Answer» (i) The enzyme pepsin digests protein in the stomach. (ii) Lipase is used to break down the emulsifying fats in the sınall intestine |
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| 21. |
What is biodiversity? Why are farests considered as "biodiversity hot spots"? List two factors responsible for causing deforestation. |
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Answer» Biodiversity is the occurrence of diverse type of organisms and their variants adapted in different environments. Forests are areas which are rich in biodiversity and are also the most threatened ones due to high degrees of exploition and human interference. The factors responsible for cansing deforestation are- (i) Industrial needs and developmental projects like building of roads, dams, etc.. (ii) Urbanisation where forests are converted into housing colonies. (iii) Reuirement of forest produce for a large number of industeires such as timber, paper lac sports euipments etc. |
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| 22. |
(a) Plants do not have any nervous system but yet, if we touch a sensitive plant, some observable changes take place in its leaves. Explain how could this plant respond to the external stimuli and how it is communicated. (b) Name the hormone that needs to be administered to (i) increase the height of a dwarf plant. (ii) cause rapid cell division in fruits and seeds. |
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Answer» Plaats have a hormonal system for controlling and co-ordinating the activities in plants. Plants respond to light, touch, gravitational force and other stimuli. They show two different lypes of movements, they are- * dependent on growth and *independent of growth. In the sensitive or 'touch - me- not' plant the leaves begin to fold up and droop an touching. It uses electrical-chemical means to convey this information from cell to cell .Some cells their shape (by changing the amount of water in them) in order for movement to happen. This type of movement is indeperident of growth called nastic movement. (b) (i) Auxin (ii) Cytokin. |
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| 23. |
A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the results in `F_(1)` progeny ? |
| Answer» All plants bear violet flowers in the `F_(1)` progeny. | |
| 24. |
Name the process and explain the type of nutrition found in green plants. List the raw materials required for this process. Given chemical equation of the mentioned process. (b) Write three events that occurs during this process. |
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Answer» (a) Green plants obtain their food by the process of photosynthesis . The mode of nutrition is called autotrophic nutrition. This of nutrition involves the intake of simple inorganic materials from the environment and use an external energy source like the sun to synthesise complex high energy orgain material. The process by which green plants make their own food (glucose) using inorganic material like carbon-dioxide and water by using sunlight energy is called photosynthesis. ` 6CO_(2) + 6H_(2)O + " Light energy " overset("chlorophyll")to underset("Glucose")(C_(6)H_(12)O_(6)) + 6O_(2)` Raw material required - (i)` CO_(2)` (ii)water (b) Events that occur during photpsynthesis (i) Absorption of sunlight energy by chlorphyll. (ii) Conversion of light energy into chemical energy and splitting of water into hydrogen and oxygen by light energy. (iii) Reducation of carbon dioxide by hydrogen to form carbohydrates like glucose by utilising the chemical energy (obtained by the transpformation of light energy). |
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| 25. |
Write any three characteristics of a good fuel. |
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Answer» Characteristics of a good fuel: (i) a good fuel should have a hight calorific value . It means it given more heat per unit mass. It sholud burn without giving out any smoke or hermful gases . So that it does not pollute air on burning. (iii) The ignition temperature of an ideal fuel should neither be too low nor too high because if the ignition temperature of the fuel is very low , then fuel will catch fire too easily and hence it will be very unsafe to use it. if the ignition temperature is too high, then it will be very difficult to light the fuel. |
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| 26. |
Explain how water and minerals are transported in plants? |
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Answer» Most plants secure their water and minerals from their roots. Minerals travel dissolved in water. Water and minerals are transported through xylem cells from the soil to the leaves . The xylem cells of roots , stem and leaves are interconnected to form a conducting channel. The root cells take ions from the soil. This creates a difference between the concentration of ions of roots and soil. Therefore, there is a steady movement of water into xylem. An somotic pressure is formed and water and minerals are transpoted from one cell to the other due to osmosis. The continuous loss of water takes place due to transpiration . |
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| 27. |
A student took a small piece of solid quick lime in a china dish and poured over it a small amount of water. List two changes he is likely to observe in the china dish immediately after pouring water. |
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Answer» When a small amount of water is poured on a piece of quick lime- it reacts vigorously with water and a hissing sound is produced and slaked lime is formed . the reaction mixture become hot as it is an exothermic reaction. |
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| 28. |
Suggest three contraceptive methods to control the size of human population which is essential for the health and prosperity of a country. State the basic principle involved in each. |
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Answer» There are three different methods of contraception : (i) Barrier methods. In these methods, physical devices as condoms, diaphragms and cervical caps are used. These devices prevent the entry of sperm in the female genital tract, thus acting as a barrier between them. (ii) Surgical methods. There are surgeries that can be carried out in males and females. In males, a small portion of the sperm duct (vas deferens) is blocked by a surgical operation . This prevents the sperms from coming out . In females, a small portion of the fallopain tubes (oviducts) is blocked by a surgical operation . It prevents the egg from reaching the uterus . In both the cases, fertilisation will not take place. (iii) Chemical methods. This category of contraceptives acts by changing the hormonal balance fo the body os that eggs are not released and fertilisation cannot occur. Females use two types of pills for preventing pregnancies , i.e., oral pills and vaginal pills. The oral pills contain hormones which stop the ovaries from releasing ovum into the fallopain tube. This is also called oral contraceptives (OC) Other contraceptive devices such as loop or the copper-T are placed in the uterus to prevent pregnancy. |
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| 29. |
Explain the term "Regeneration" as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra. |
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Answer» Regeneration is a mode of asexual reproduction in some organisms. The process of getting back a full organism from its body parts is called regeneration. The simple multicellular animals like hydra and planaria show regeneration. Regeneration in hydra: If the body of hydra gets cut into a number of pieces, then each body piece can regenerate into a complete hydra by growing all the missing parts. The regeneration of an organism from its cut body part occurs by the process of growth and development. The cells of cut body parts divide rapidly to make a ball of cells. The cells then become specialised to form different types of tissues which again form various organs and body parts. |
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| 30. |
Mention the types of mirrors used as (i) rear view mirrors, (ii) shaving mirrors. List two reasons to justify your answers in each case. |
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Answer» (i) Convex mirror is used as rear view mirror in vehicles because it always produces an erect image of the objects, the image formed in a convex mirror is highly diminished thus it gives a wide field of view. (ii) Concave mirrors are used as shaving mirrors because when the face is held within the focus of a concave mirror, then an enlarged image of the face is seen in the concave mirror. This helps in making a smooth shave. |
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| 31. |
What is the difference between soaps and detergements ? State in brief the cleaing action of soaps is removing an oily spot from a fabric. Why are soaps not very effective whene a fabric is washed in hard water ? How is this problem resolved ? . |
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Answer» Difference betwern soaps and detergents. See Q. 12, 2014-15 (Delhi). Soaps are not effective when a fabric is washed in hard water. Hardness of water is due tothe presence of `Ca^(2+)` and `Mg^(2+)` ions. These ions react with soaps to form white precipitates called scum. This scum sticks to the surface of the clothes and hence soaps are not very effective when a fabric is washed. This problem can be solved by using detergents as they are more soluble in hard water and have better cleansing actions. |
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| 32. |
The elements of the third period of the Periodic Table are given below: (a) Which atom is bigger, Na or Mg? Why? (b) Identify the most (i) metallic and (ii) non-metallic element in Period 3. (c ) Which is more non-metallic, S or Cl? (d) Which has higher atomic mass, Al or Cl? |
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Answer» (a) Na is bigger than Mg because on moving from left to right in a period, the atomic number of elements increases which means that the number of protons and electrons in the atom increases. ( The extra electrons being added to the same shell). (b) (i) Most metallic element is Na. Most non-metallic element is Cl, Because on moving from left to right in a period the nuclear charge increase thus the vlence electrons are pulled in more strongly by the nucleus and it becomes more and more difficult for the atoms to lose electrons so tendency of atoms to lose electrons (i.e., metallic character) decreases on moving from left to right in a period. On the other hand, due to increased nuclear charge, it becomes easier for the atoms to gain electrons. So the tendency to gain electrons (i.e., non-metallic character) increase on moving from left to right left to right in a period. (c) Cl is more non-metallic from S because on moving from left to right in a period, nuclear charge increase so the tendency to gain electrons increases (i.e., non-metallic character). (d) Cl has higher atomic mass because on moving from left to right in a period, atomic number increase. Simultaneously, atomic mass increases. |
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| 33. |
What is the main difference between sperms and eggs of humans ? Write the importance of this difference. |
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Answer» The main difference between sperms and eggs of humans is that half of the sperms of a male ( father ) will have X chromosomes and the other half will have Y chromosomes. All the eggs of females ( mother) will have only X chromosomes. Importance. If the father contributes X sex chromosome, at fertilisation through his sperm, the baby born will be a girl. On the other hand, if the father contributes a Y sex chromosome at fertilisation through his sperm, then the baby born will be a boy. Therefore the sperm determines the sex of the child. |
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| 34. |
What are homologous series of carbon compounds ? Write the molecular formula of two consecuative members of homologous series of aldehydes. State which part of these compounds determines their (i) physical and (ii) chemical properties. |
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Answer» Homologous series. A series of carbon compounds in which the same functional group substitutes for hydrogen on a carbon chain is called a homologous series. There is a difference of `-CH_(2)` in the molecular formulae of two nearest compounds of a homologous series. Each such series has same general molecular formula and has a general scientific name. There is a difference of `14 mu` ( unified mass) in the molecular masses of two nearest compounds of a series. Members of homologous seris of aldehydes `:` H - CHO Methanal `CH_(3) - CHO` Ethanal `C_(2)H_(5) -CHO` Propanal (i) The carbon-chain attached to aldehyde group , i.e., `( H-, CH_(3)- , C_(2)H_(5))` determine the physical properties. (ii) The functional group attached to all aldehydes ( -CHO) determines the chemical properties. |
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| 35. |
Why are homologous series of carbon compounds so called? Write chemical formula of two consecutive members of a homologous series and stte the part of these compounds that determines their (i) physical properties, and (ii) chemical properties. |
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Answer» All the organic compounds having similar structures show similar properties and theyare put together in the same groups of series called homologous series. For example, all the alkanes have similar structures with single covalent bonds and show similar chemical properties so they are grouped together in a homologous series having general formula `C_(n)H_(2n+2).` The two consecutive members of a homologous series are methane `CH_(4)` and ethane `C_(2)H_(6)`. (i) Any two adjacent homologues differ by 1 carbon and 2 hydrogen atoms in their molecualr formulae. So the difference in molecular masses of any two adjacent homologues is 14 u. Thus the members of a homologous series show a gradual change in their physical properties with increas in molecular mass. (ii) All the compounds of a homologous series show similar chemical properties because they have similar structures and similar bonding. |
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| 36. |
(a) Give the evidence that the birds have evolved from reptiles. Insects, octopus, planaria and vertebrates posses eyes. Can we group these animals together on the basis of eyes that they possess? Justify your answer giving reason. |
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Answer» (a) A fossil bird called Archaeopteyx looks like a bird but it has many features which are found in reptiles. Archaeopteryx has featured wings like birds but teeth and tail like those of reptiles. Therefore Archaeopteryx is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles. (b) Insects, octopus, planaria and vertebrates posses eyes but these animals can not be put togther on the basis of eyes because the structure of eyes in each of there organisms is different which suggests their separate evolutionary origins. Thus all these animals are put in different groups. |
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| 37. |
(i) Calculate the current through a lamp of 25 W operating at 250 V. (ii) Why elements of electrical heating devices are made up of alloys? |
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Answer» (i) Power of the lamp, P = 25 W Potential difference, V = 250 V Current, I = ? Formula `=VxxI" "therefore " "25=250xxI` `therefore "Current", I =(25)/(250)=(1)/(10)=0.1 A` (ii) The heating elements of electrical heating appliances are made up of nichrome alloy because: nichrome has very high resistivity due to which it produces a lot fo heat on passing current. nichrome does not undergo oxidation easily even at high temperature, it can be kept red hot without burning. |
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| 38. |
List two different functions performed by pancreas in our body. |
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Answer» Functions of pancreas: (i) Secretes enzyme trypsin for the breakdown of proteins. (ii) Secretes hormone insulin to regulate sugar level in the blood. |
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| 39. |
What is feedback mechanism of hormonic regulation? Take the example of insulin to explain this phenomenon. |
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Answer» The mechanism through which the timing and amount of hormone released and regulated in our body, by the glands is called feedback mechanism of hormonic regulation. For example, if the sugar level in the blood rises, this is detected by the cells of the pancreas which respond by producing more insulin to oxidize the sugar. As the blood sugar level falls, insulin secretion is reduced automatically. |
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| 40. |
Why do raisins absorb water when soaked in water ? Explain the phenomenon. |
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Answer» Raisins absorb water due to the process of endosmosis. Water moves from semi permeable membrane of raisin, i.e., from hypotonic solution to the hypertonic solution of raisin cell sap. |
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| 41. |
With the help of suitable examples, explain why certain traits cannot be passed on to the next generation .What are such traits called ? or "A trait may be inhertited, but may not be expressed. " Justify this statement with the help of a suitable example. |
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Answer» A trait of an organism which develops in response to the environment and brought in the non-reproductive tissues can not be passed on to the DNA of the germ cells. Such traits are called acquired traits. An individuals cannot pass these traits to its progency as these traits cannot be passed on to the DNA of ther germ cell. Example `:` (i) If a beetle does not get sufficient food for a considerable time, its weight will reduce due to starvation. The low weight in an acquired trait. (ii) Cut tail of a mouse. or Mendel crossed pure-bred tall pea plants with pure-bred dwarf pea plants and found that only tall pea plants were produced in the `F_(1)` generation . Mendel then crossed the tall pea plants of `F_(1)` generation and found that tall plants and dwarf plants were obtained in the `F_(2)` generation in the ratio of `3:1`. This experiment shows that the traits of dwarfness had not been lost but it was merely concealed in the `F_(1)` generation. Thus "A trait may be inherited , but may not be expressed. " |
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| 42. |
In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? Plants `to` Deer `to ` Lion |
| Answer» 10,00,000 Joules. | |
| 43. |
What is an ecosystem ? |
| Answer» Ecosystem is a unit of biosphere where interaction between biotic community and abiotic factors of an area of place takes place with each other. | |
| 44. |
What is sustainable management ? Why is reuse considered better in comparison to recycle ? |
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Answer» Sustainable management means the judicious use of the natural resources by the present generations so that these resources are also available for the future generations. In the recycling of materials some energy is used and also harmful gases are produced which pollute the environment, while reuse of materials does not consume energy. |
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| 45. |
List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over the past 50 years in our country. |
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Answer» The significance of reproductive health of society are: (i) Regular medication and check-ups have led to development of reproductive health . Healthy mothers given birth healthy children. (ii) Reproductive health should be maintained in order to prevent sexually transmitted diseases (STDs). (iii) Farmily planning by using various constraceptives enables a couples to decide on the number of children they want to have and when to have them . If a couples has less number of children they can provide good food, clothes and education to each child So, a small family is a happy family. (iv) Having fewer children also keeps the mother in good health. This will reduce the cases of maternal mortality as well as new born mortailty. Areas which have improved: (i) Better family planning has led to reduction in family size and better econmic stability. (ii) Decrease in STD cases due to more awareness and winer use of contraceptives . |
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| 46. |
What is DNA copying ? State its importance. |
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Answer» A process in which a DNA molecule produces two similar copies of itself in a reproducing cell through chemical reaction is a called DNA copying. (i) It transmits the characteritics from parents to the next generation ( offspring ) (ii) It causes increased variations in the population. |
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| 47. |
Write the name , sybbol and electronic configuration of an element X whose atomic number is 11. |
| Answer» Name of the element: sodium, symbol: Na, Electronic configuration: 2, 8, 1 | |
| 48. |
Identify the acid and base which form sodium hydrogen carbonate. Write chemical equation in support of your answer. State whether this compound is acidic, basic or neutral. Also write its pH value. |
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Answer» Sodium hydrogen carbonate is formed by a chemical reaction between a weak acid- carbonic acid and strong base - sodium hydroxide. `NaOH + H_(2)CO_(3) rarr Na HCO_(3) + H_(2)O` The compound formed is weak basic in nature and has pH value slightly above 7. |
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| 49. |
Write the main difference between an acid and a base. With the help of suitable examples explain the term neutralization and the formation of- (i) acidic, (ii) basic and (iii) neutral salts. |
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Answer» Acids are sour in taste and change the colour of the blue litmus to red. Their pH is less Ther reaction between an acid and a base to give a salt and water is known as a neutralisation reaction. In general, a neutralisation reaction can be written as Acid + Base `rarr` Salt + Water Example: `NaOH (aq) + HCl (aq) rarr NaCl (aq) + H_(2)O(l)` (i) When neutralisation of a strong acid with a weak base takes place, it leads to the formation of acidic salt. Example: `H_(2)SO_(4) +CuO to CuSO_(4) + H_(2)O` (ii) When neutralisation of a weak acid with a strong base takes place, it leads to the formation of basic salt. Example: `NaOH + CH_(3) COOH rarr CH_(3) COONa + H_(2)O` When neutralisation of a strong acid with a strong base takes place, it leads to the fromation of neutral salt. Example: `NaOH + HCl rarr NaCl +H_(2)O` NaCl is a neutral salt. |
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| 50. |
A bag contains 15 white and some black balls. If the probability ofdrawing a black ball from the bag is thrice that of drawing a white ball,find the number of black balls in the bag. |
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Answer» Let the number of black balls be n. Total no. of balls=15+n according to the question=>`n/(n+15)=45/(n+15)` thus n=45. |
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