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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.
| 51. |
Write two examples each of sexually transmitted diseases caused by (i) virus, (ii) becteria. Explain how the transmission of such diseases be prevented? |
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Answer» Sexually transmitted diseases caused by (i) Virus: (1) AIDS (Acquired lmmuno Deficiency Syndrome), (2) Genital warts (ii) Bacteria : (1) Gonorrhoea, (2) Syphilis Transmission of such diseases can be prevented by the following ways: - Screening tests for blood donors - Mutually faithful monogamous relationships - Educating people in high risk groups - Using condoms,etc. |
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| 52. |
Write three types of blood vessels. Give one important feature of each. |
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Answer» Three types of blood vessels are: 1. Arteries - Arteries carry the oxyhenated blood away from the heart to the various organs of the body. 2. Veins - Veins carry deoxygenated blood from different organs of the body back to the heart. 3. Capillaries - Capillaries are the smallest vessels where exchange of material between the bolld and surrounding cells takes place. |
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| 53. |
Why is epidermal peel generally taken from lower surface of the leaf? |
| Answer» In dicot plants stomata are found in lower surface only, hence peel is taken from the lower surface . As stomata are present on both the surfaces of leaf in monocot plants so the peel can be taken from either surface. | |
| 54. |
To find the image-distance for varying object-distances in case o fa convex lens, a student obtains on a screen a sharp image of a bright object places very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image on the screen. (a) In which direction-towards or away from the lens, does he move the screen to focus the object ? (b) What happens to the size of image - does it increase or decrease? (c ) What happen when he moves the object very close to the lens ? |
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Answer» (a) He moves the screen away from lens to focus the object. (b) The size of the image increases. (c ) When the object is places very close to the lens, then image will be formed on the screen. As now image formed is erect and virtual. |
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| 55. |
Match the important chemical given in column (A) with the chemical fomulae given in Column (B). `{:("Column (A), Column (B)"),("(a) Plaster of paris, (i)" ca(OH)_(2)),("(b) Gypsum (ii)"CaSO_(4) .(1)/(2)H_(2)O),("(c) bleaching powder (iii)" CaSO_(4).2H_(2)O),("(d) Slaked lime (iv)"CaOCL_(2)):}` |
| Answer» `{:("Column (A), Column (B)"),("(a) Plaster of paris, (ii)" caSO_(4).(1)/(2)H_(2)O),("(b) Gypsum (iii)"CaSO_(4) .2H_(2)O),("(c) bleaching powder (iv)" CaOCl_(2)),("(d) Slaked lime (i)"Ca(OH)_(2)):}` | |
| 56. |
A circuit has a line of 5 A. How many lamps of rating 40W,220V can simultaneously run on this line safely ? |
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Answer» `I = 5A` No. of lamps `=n` Power , `P = 40W` `V=220 V` Power of 1 bulb `=40 W` Power of n bulbs `= 40 n ` watts `P = V xx I` `4n = 220 xx 5` `implies n = ( 220 xx 5)/(40) = (55)/(2) = 27.5` `:. `No . of lamps of `=27` |
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| 57. |
Explain the effect on the magnetic field produced at a point in a current carrying circular coil due to `:` (i) increase in the amount of current flowing through it. (ii) increase in the distance of point from the coil (iii) increase in the number of turns of the coil. |
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Answer» (i) The magnitude of magnetic field produced by a current carrying circular coil at a point is directly proportional to the current flowing through the circular coil . Thus as the amount of current flowing through the circular coil increases, the magnetic field produced at a point in a circular coil increases. (ii) Magnetude of magnetic field produced at a point in a current carrying circular coil is inversely proportional to the distance of point from the coil. Thus the magnetic field produced at a point decreases as the distance increases from the coil. (iii) The magnetic field produced by a current carrying wire at a given point depends directly on the current passing through it. Therefore, if there is a circular coil having n turns, the field produced in n times as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to such turns then just adds up . |
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| 58. |
Explain the following: (a) Sodium chloride is an ionic compound which does not conduct electricity in solid state whereas it does conduct electricity in molten state as well as in aqueous solution. (b) Reactivity of aluminium decrease if it is dipped in nitric acid. (c) Metals like calcium and magnesium are never found in their free state in nature. |
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Answer» (a) Sodium chloride does not conduct electricity in solid state whereas it does conduct electricity in molten state as well as in aqueous solution. This is because in solid state movement of ions is not possible due to rigid structure. Movement of ions is what causes electricity. In molten and aqueous state, ions are free to move and so they conduct electricity. (b) Reactivity of aluminium decreases if it is dipped in nitric acid, because nitric acid is a strong oxidising agent. As a result, when aluminium is dipped in nitric acid, a layer of aluminium oxide is formed which prevents further reaction of aluminium. (c) Metals like calcium and magnesium are never found in their free state in nature. This is because they are highly reactive metals and form compounds with almost all elements. |
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| 59. |
Decomposition reactions require energy either in the form of the heat or light or electricity for breaking down the reactants. Write one equations each for decomposition reactions where energy is supplied in the form of heat, light and electricity . |
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Answer» Thermal decomposition When calcium carbonate is heated, it decomposes to given calcium oxide and carbon dioxide. `CaCO_(3)(s) overset("Heat")rarr CaO(s) + CO_(2)(g)` When silver chloride is exposed to light it decomposes to form silver metal and chlorine gas. `2AgCl (s) overset("Light")rarr 2Ag(s) + Cl_(2)(g)` When electric current is passed through acidified water, it decomposes to give hydrogen gas and oxygen gas. `2H_(2)O (l) overset("Electricity")(rarr) 2H_(2)(g) + O_(2)(g)` |
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| 60. |
Give any four precautions taken by a student to perform an experiment to determine the resultant resistance of two resistors when connected in series. |
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Answer» (i) Clean the ends of the connecting wires by sand paper. (ii) The connections should be tight. (iii) Close the key (K) only when readings are to be taken. (iv) Zero errors and the ranges of the ammeter and voltmeter should be noted. |
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| 61. |
What are the precautions taken to prepare a temporary mount of a leaf peel to show its stomata? |
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Answer» Precautions taken to prepare a temporary mount of a leaf peel: (i) The epidermal peel should be taken from a freshly plucked leaf. (ii) Always hold the slide by its edge to avoid making the slide dirty. (iii) Always use a brush to transfer the peel from petri dish to the slide. (iv) Curling of peel must be avoided. (v) The peel should be mounted in the centre of the slide. (vi) The peel should not be allowed to dry. (vii) Always keep the cover slip gently to avoid the entry of air bubbles. |
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| 62. |
A student has to trace the path of way of light through a glass prism. List four precautions he should observe for better results. |
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Answer» Precautions to be observed while tracing the path of ray of light through a glass prism: (i) A sharp pencil shold be used for drawing the boundary of the glass prism. (ii) The seperation between the two pins should not be less than 5cm. (iii) The pin should have sharp tips and fixed vertically. (iv) Proper arrows should be marked to indicate incident, refracted and emergent ray. |
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| 63. |
A metal X ,which is used in thermit process , when heated with oxygen gives an oxide Y which is amphoteric in nature . Identify X and Y. Write balanced chemical equation of the reaction of oxide Y with hydrochloric acid and sodium hydroxide . |
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Answer» When aluminium is heated in oxygen it forms aluminium oxide which is amphoteric in nature . `4Al + 3O_(2) to 2Al_(2)O_(3)` X is aluminium . Y is aluminium oxide Reaction of Aluminium oxide with hydrochloric acid: `Al_(2)O_(3)+6HCl to 2AlCl_(3)+3H_(2)O` REaction of Aluminium oxide with sodium hydroxide `Al_(2)O_(3)+2NaOH to 2NaAlO_(2)+H_(2)O` |
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| 64. |
"Conversion of ethanol of ethanoic acid is an oxidation reaction . " Justify this statement giving the relevant equation for the chemical reaction involved . |
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Answer» `CH_(3)CH_(2) underset( " Or Acidified " K_(2)Cr_(2)O_(7)+"Heat") overset("Alkaline " KMnO_(4)+ "Heat")toCH_(3)COOH+H_(2)O` Here ethanol is converted into ethanoic acid in the presence of oxidising agents ( such as `KMnO_(4) or K_(2)Cr_(2)O_(7)`) , Thus , since the conversion involves the addition of oxygen to ethanol , it is an oxidation reaction . |
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| 65. |
In a school laboratory the students are studing the properties of ethanoic acid through certain experiments. How can they test its acidic nature ? Give two tests . |
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Answer» (i) Ethanoic acid turns blue litmus solution to red. (ii) Ethanoic acid gives orange colour with universal indicator . (iii) Ethanoic acid remains colourless in phenolphthalein. (iv) On adding solid sodium carbonate or sodium hydrogen carbonate, brisk effervescence is observed . |
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| 66. |
Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment. |
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Answer» Plastic bags are non-biodegradable which can no t be broken down into-poisonous substances in nature. Plastic bags are the main cause of sewer blockages as plastic bags are not decomposed by micro-organisms. Plastic bags if eaten by stay animals (like cows) can block their alimentary canal. Two alternatives : (i) We should take over own jute or cloth bags while going for purchasing articles from the market. (ii) Disposable paper cups should be used for serving tea in trains instead of plastic cups. (iii) Shopkeepers can use paper bags instead of plastic bags. |
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| 67. |
An object of height 6 cm is placed perpendicular to the principal axis of a concave axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm. |
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Answer» Height of the object, `h_(1) = 6 cm` Focal length of the concave mirror, `f= -5 cm` Position of the image, `v= ?" Size of the image , " h_(2)=?` Object distance , `u= -10 cm` According to lens formula: `(1)/(v)-(1)/(u)=(1)/(f) rArr (1)/(v)-(1)/(-10)=(1)/(-5)rArr (1)/(v)+(1)/(10)=(-1)/(5)` `rArr (1)/(v)= (-1)/(5)-(1)/(10)=(-2-1)/(10)=(-3)/(10) therefore v = (-10)/(3) = -3.3 cm` `(h_(2))/(h_(1)) = (v)/(u) rArr (h_(2))/(6)= (cancel(-)(10)/(3))/(cancel(-)10)` `rArr (h_(2))/(6)=(10)/(3xx10)=(1)/(3) rArr h_(2)=(6)/(3) therefore h_(2) = + 2 cm` Thus the image is formed at a distance of 3.3 cm from the concave lens. The negative (-) sign for image distance shows that the image is formed on the left side of the concave lens (i.e., virtual). The size of the image is 2 cm and the positive (+) sign for hand image shows that the image is erect. Thus a virtual, erect, diminished image is formed on the same side of the object (i.e., left side). |
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| 68. |
A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from the optical centre of the lens 12 cm and its sharp image is formed at a distance of 24 cm from it on a screen on the lens, in the which ways (towards the lens or away from the lens) will he have to move the screen to get a sharp image of the object on it again? How will the magnification of the image be affected ? . |
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Answer» (a) The screen should be moved towerds the lens to get a sharp image of the object again. (b) Magnification of the image decreases on moveing the object away from the lens. |
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| 69. |
Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device. |
| Answer» Concave mirrors are used in the design of solar furnaces. When a solar furnace is placed at the focus of a large concave mirror (called reflector), it focuses a parallel beam of light on the furnace, as a result a temperature is achieved after some time. | |
| 70. |
In an experiment , to study the dependence of potential difference (V) on the electric current (I) across a conductor (resistor), if the circuit is on for long time, then -select two correct options from the following: (i) Zero error of an ammeter will be changed. (ii) Zero error of a voltmeter will be changed . (iii) Value of a resistance will be changed. (iv) Resistor will be heated. |
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Answer» (i) Value of resistance will be changed. (ii) Resistor will be heated. |
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| 71. |
What is meant by speciation ? List four factors that could lead to speciation . Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Give reason to justify your answer. |
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Answer» Speciation . The process by which new species develop from the existing species by evolution or any genetic modification of previous species is known as speciation. (i) Geographical isolation of a population caused by various types of barriers like mountain ranges, rivers, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separatiion groups of population. (ii) Genetic drift caused by drastic in the frequencies of particular genes by chance alone. (iii) Variatios caused in individuals due to natural selection. (iv) Drastic change in the genes or DNA called mutation is also a cause of speciation. Reproductive isolation can not be a major factor for the speciation of a self-pollinating plant species as it does not depend on any other plant for its reproduction process. |
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| 72. |
Write the relation between electric power (W ) of a device with potential differnece (Volt) across it and current ( amp ) flowing through it. |
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Answer» The power (P) in watts is found by multiplying the potential differnece ( V ) in volts by the current (I) in amperes. Electric power `=` Potential differnece `xx` Current `P= V xx I` |
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| 73. |
Write chemical equations for the following reactions: (i) Calcium metal reacts with water. (ii) Cinnabar is heated in the presence of air. (iii) Manganese dioxide is heated with aluminium powder. (b) What are alloys? List two properties of alloys. |
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Answer» (i) `underset("Calcium")(Ca(s)) + underset("water")(2H_(2)O(l)) rarr underset("Clacium hydroxide")(Ca(OH)_(2)(aq))+ underset ("Hydrogen gas")(H_(2)(g))` (ii) `underset ("Cinnabar")(2HgS(s))+ underset("from air") underset ("Oxygen") (3O_(2)(g)) overset("heat")(rarr) underset ("Cinnabar oxide") (2HgO(s)) + underset ("dioxide") underset("Sulphur") (2SO_(2)(g)` (iii) `underset("dioxide")underset ("Manganese") (3MnO_(2)(s)) + underset("Aluminium") (4Al(s)) rarr underset("metal") underset("Manganses")(3Mn(l))+ underset ("oxide") underset ("Aluminium") (2Al_(2)O_(3)(s))+ Heat` (b) Alloys are homogeneous mixtures of two or more metals of a metal and a non-metal The properties of an alloy are different from the properties of the constituent metals. In general- `*` alloys are stronger than the metals from which they are made. `*`alloys are mor resistant to corrosion. |
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| 74. |
What is meant by electric circuit ? Why does electric current start flowing in a circuit the moment circuit is complete ? When do we say that the potential difference across a conductor in a circuit is 1 volt ? Calculate the potential difference between the two terminals of a battery if 12 joules of work is done in transferring 2 coulombs of charge. |
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Answer» `*` A continuous conducting path consisting of wire and other resistances (like electric bulb, etc.) and a switch, between the two terminals of a cell or a battery along which an electric current flows is called an electric circuit. `*` It is the potential difference between the ends of the wire which makes the electric charges (or current) to flow in the wire. The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of electric charge from one point to another. Thus, 1 volt `=(1 "joule")/(1 "coulomb") " " or " "` 1 volt `=(1J)/(1C)` or 1 J/C `* V=?" "W=12 J " "Q=2C` Now, `V=(W)/(Q)=(12J)/(2C)=6` volts |
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| 75. |
Record your observations when a stained a mounted leaf peel is viewed by you under high power (45`xx`) microscope. |
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Answer» (i) The process (stomatal process) in which stomatal pores are clearly seen. (ii) Each stomata has two kidney shaped cells (guard cells) having one nucleus and many chloroplasts each. |
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| 76. |
(a) Why does calcium start floating when added to water? (b) Most of the metals do not give hydrogen while reacting with nitric acid. Why? (c ) Write equation for the reaction of iron with steam. Name the compound of iron obtained. |
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Answer» (a) The reaction of calcium with water is less violent. The heat evolved is not sufficient for hydrogen to catch fire. `Ca(s)+2H_(2)O(l) to Ca(OH)_(2)(aq) +H_(2)(g)` Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. (b) Most of the metals do not give hydrogen while reacting with nitric acid because `HNO_(3) ` is a strong oxidising agent. It oxidises the `H_(2)` produced to water `(H_(2)O)` adn itself gets reduced to any of the nitrogen oxides `(N_(2)O,NO,NO_(2)).` (c ) Iron reacts with steam to form iron oxide and hydrogen `3Fe (s)+4H_(2)O(g) to Fe_(3)O_(4)(s)+4H_(2)(g)` |
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| 77. |
Solid calcium oxide was taken in a container and water was added slowly to it. (i) State two observations made in the experiment. (ii) Write the balanced chemical equation of this reaction. or Write balanced chemical equations for the following reactions `:` (a) dilute sulphuric acid reacs with aluminium powder. (b) dilute hydrochloric acid reacts with sodium carbonate. (c ) Carbon dioxideis passed through lime water. |
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Answer» (i) Solid calcium oxide was taken in a container and water added to it. Observation `:` The mixture produces a hissing sound. The beaker feels to be quite hot. (ii) `underset("(lime)")underset("Calcium oxide")(CaO(s))+H_(2)O rarr underset("(slaked flame)")underset("Calcium hydroxide")(Ca(OH)_(2))+"Heat"` (a) `2Al(s) +3H_(2)SO_(4)(aq)rarr underset("Aluminium sulphate")(Al_(2)(SO_(4))_(3)(aq))+3H_(2)uarr` (b) `underset("Sodium carbonate")(Na_(2)CO_(3)(s)) +2HCl(aq) rarr 2NaCl(aq) +CO_(2)+H_(2)O` (c ) `CO_(2)(g) +underset("Lime water")(Ca(OH)_(2)(aq))rarr underset("(White ppt makes lime water milky)")(CaCO_(3)(s))+H_(2)O` |
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| 78. |
Name two salts each of calcium and magnesium which make the water hard? |
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Answer» Calcium chloride - `CaCl_(2) " " ` Magnesium chloride - `MgCl_(2)` Calcium sulphate - `CaSO_(4) " " ` Magnesium sulphate - `MgSO_(4)` |
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| 79. |
(a) How is pH paper used to find the pH of a solution? (b) The pH value of water is 7. What will be the pH value of (i) aqueous solution of sodium hydroxide and (ii) dil. HCl. |
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Answer» (a) With the help of a dropper one drop of the solution a placed on the strip of the pH paper. The colour developed on the pH paper is compared with the colour and the corresponding pH value given on the chart of the pH paper. (b) aqueous solution of sodiium hydroxide is alkaline so its pH will be more than 7. dil HCl is acidic so its pH value will be less than 7. |
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| 80. |
(a) How is pH paper used to find the pH of a solutions? (b) The pH value of water is 7. What will be the pH value of (i) aqueous solution of sodium hydroxide and (ii) dil HCl. |
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Answer» (a) With the help of a dropper one drop of the solution is placed on the strip of the pH paper. The colour developed on the pH paper is compared with the colour and the corresponding pH value given on the chart of the pH paper. (b) `*` aqueous solution of sodium hydroxide is alkaline so its pH will be more than 7. `*` dil HCl is acidic so its pH value will be less than &. |
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| 81. |
How is the concentration of hydronium `(H_(3)O^(+))` ions affected when a solution of an acid is diluted? |
| Answer» When an acid solution is diluted with then concentration of `(H_(3)O^(+))` ions gets decreased. | |
| 82. |
Explain giving justification the trends in the following properties of elements, on moving , from left to right in a period, in the Modern periodic Table. (a) Variation of valency. (b) Change of atomic radius . (c) Metallic to non-metallic character. (d) Electronegative character. (e) nature of oxides. |
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Answer» Properies of elements on moving from left to right in a period. (a) Valency, ON moving from left to right in a period, the valency of elements increases from 1 to 4 and then decreases to zero. This is because the first element of every period has 1 valence electron and the last element in every period has 8 valence electrons except for the first period. (b) Atomic radii. On moving from left to right in a period, the size of the atoms decreases. This is because on moving left to right in a period, the atomic number of elements increases. It means the number of protons and electrons in the atoms increase and extra electrons are being added to the same shall. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of atom decreases. (C) Metallic to non-metallic character. On moving from left to right in a period, the metallic charater of elements decreases but the non-metallic character increases. Since the size of the atom decreases on moving from left to right , the removal of electrons from the outermost shell becomes difficlt . On the other hand, addition of electrons becomes easy. (d) Electronegative character. In increases as we move from left to right along the period, As we got from left to right in the periodic table, the reactivity reduces as a result giving away of electrons reduces and taking electrons increases. Henc, electronegativity increases. (e) Nature of oxides. On moving from left to right in a period , the bais nature of oxides decreas3es and the acidic nature of oxides increases. |
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| 83. |
An element P(atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reasons : (a) Write the positions of P and Q in the Modern Periodic Table. (b) Write the molecular formula of the compound when P reacts with Q. |
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Answer» Element P : Electronic configuration : 2, 8, 8, 2 So, element P belongs to `4^(th)` period and group 2, as it has four shells and 2 valence electrons. Element Q : Electronic configuration : 2, 8, 7 So element Q belongs to `3^(rd)` period and group 17, as it has three shells and seven valence electrons. Molecular formula of compound will be `PQ_(2)`. As valency of P is 2 and valency of Q is one. |
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| 84. |
A gas is liberated immeiately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate power in a test tube. Name the gas and describe the test that confirms the identify of the gas. |
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Answer» The liberated gas is `CO_(2)` gas. The test that confirms the identity of the gas is its test with lime water. `CO_(2)` gas turns the lime water milky. `underset("Lime water")(Ca(OH)^(2) (aq)+CO_(2)) rarr underset("White ppt")(CaCO_(3) (s))+H_(2)O` |
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| 85. |
What type of material is formed when aqueous solutions of sodium sulphate and barium chloride are mixed. Give the balanced chemical equation involved. Name the type of reaction it is ? |
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Answer» `**" "`A white precipitate of `BaSO_(4)` will be formed. `**" "Na_(2)SO_(4) (aq)+BaCl_(2)(aq) rarr BaSO_(4) (s)+2 NaCl (aq)` `**" "`It is a double displacement reaction. |
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| 86. |
Write the balanced chemical equation with the state symbols of the following reaction : Solutions of Barium chloride and sodium sulphate in water react to give insoluble Barium sulphate and the solution of soium chloride. |
| Answer» `BaCl_(2) (aq) + Na_(2)SO_(4) (aq) rarr BaSO_(4)(s) + 2NaCl(aq)` | |
| 87. |
These resistors of `10Omega,15Omega and 5Omega` are connected in parallel. Find their equivalent resistance. |
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Answer» `R_(1)=10Omega " "R_(2)=15Omega" "R_(3)=5Omega` `R_(1), R_(2) and R_(3)` are connected in parallel then equivalent resistance ® is given by `(1)/(R)=(1)/(R_(1))+(1)/(R_(2))+(1)/(R_(3))` `(1)/(R)=(1)/(10)+(1)/(15)+(1)/(5)=(3+2+6)/(30)=(11)/(30)` `therefore` Equivalent resistance , `R=(30)/(11)=2.72Omega` |
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| 88. |
Two resistance `R_(1) = 10` ohm and `R_(2) = 10` ohm are to be connected with 20V battery. Out of which of the following maximum current will flow. Calcuate its magnitude. |
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Answer» In all the three cases, the same current will be flowing as in all the three cases. Both the resistors are combined in series. `R_(1)=10 Omega" " R_(2)=10Omega` Resultant `R=R_(1)+R_(2)=10+10=20Omega` `V=20 V` `I=(V)/( R) = (20)/(20) = 1A` |
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| 89. |
Define 1 ohm resistance. A student has a resistance wire of 1 ohm. If the length of this wire is 50 cm, to what length he should stretch it uniformly so as to obtain a wire of ` 4 Omega` resistance? Justify your answer . |
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Answer» 1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of ampere flows through it. Resistance, 1R_(1) = 1 Omega, L_(1) 50 cm = (50)/(100) m = (1)/(2)`m ` Required resistance, `R_(2) = 4 Omega` Required length, `L_(2) = ?` R `propto` L `(R_(1))/(L_(1)) ` Constant, `(R_(2))/(L_(2))` = Constant `(R_(1))/(L_(1)) = (R_(2))/(L_(2)) = (1)/(1//2) = (4)/(L_(2)) rArr (1xx 2)/(1) = (4)/(L_(2))` `L_(2) = (4)/(2) therefore L_(2) = 2n` |
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| 90. |
What is pollination? How does it occur in plants? How does pollination lead to fertilization ? Explain. |
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Answer» The transfer of pollen grains from anthers (male sexual parts) of a flower to the stigma part of the pistil (female sexual part) is known as pollination. Pollination is done by insects, birds, wind and water. Pollination can occur in two ways: (i) Self pollination. When the pollen grains from the anther of a flower are tansferred to the stigma of the same flower or another flower on the same plant, it is called self pollination. (ii) Cross pollination. When the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another similar plant, it is called cross pollination. When a pollen grain falls on the stigma of the carpel, it grows a pollen tube downwards through the style towards the female gamete in the ovary. A male gamete moves down the tube. When the pollen tube enters the ovule, its tip bursts open and male gamete comes out of the pollen tube and combines with the nucleus of the female gamete and forms zygote. This process is known as fertilization. |
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| 91. |
Pure iron is soft and stretches easily when hot (a) How does this property of iron change when: (i) small amount of carbon is mixed with it? (ii) nickel and chromium are mixed with it? (b) Define an alloy. How is an alloy prepared? (c) An alloy has low melting point and is therefore used for electrical fuse. Name the alloy and write its constituents. |
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Answer» (i) When small amount of carbon is mixed with iron, it becomes an alloy that is called steel. The carbon present in pig iron makes it brittle and therefore, it cannot be used for structural purposes. (ii) When iron is mixed with chromium and nickel, then stainless steel is obtained. Stainless steel does not rust at all. Stainless steel is used for making cooking utensils, knives, scissors and surgical instruments etc. (b) Alloy: An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. An alloy is generally prepared by heating the mixture of the metal (or metal and non-metals) to the molten state and then cooling the mixture to solidify at room temperature. (c) A fuse wire is made up of an alloy of tin and copper or tin and lead (composition: 63% tin and 37% lead). |
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| 92. |
We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make people realise that the improper disposal of waste is harmful to the environment. |
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Answer» (i) When the domestic waste is decomposed by the action of micro-organisms then it becomes the breeding place of files and mosquitoes. Files and mosquitoes are the carrier and vector of many dangerous diseases. So some posters related to the spread or such diseases can be pasted on the walls in public places to create awareness. (ii) There should be a strict fine imposed by the sanitary officer from the families which throw their domestic waste on the roads. |
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| 93. |
(a) Classify the following reactions into different types : (i) `AgNO_(3)(aq)+NaCl(aq)rarrAgCl(s)+NaNO_(3)(aq)` (ii) `CaO(s)+H_(2)O(l)rarrCa(OH)_(2)(aq)` (iii) `2KClO_(3)(s)overset(Delta)rarr2KCl(aq)+3O_(2)(g)` (iv) `Zn+CuSO_(4)rarrZnSO_(4)+Cu` (b) Translate the following statement into a balanced chemical equation: 'Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate'. |
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Answer» (a) (i) Double displacement reaction (ii) Combination reaction (iii) Decomposition reaction (iv) Displacement reaction (b) `underset("chloride")underset("Barium")(3BaCl_(2))+underset("Sulphate")underset("Aluminium")(Al_(2)(SO_(4))_(3))rarrunderset("Chloride")underset("Aluminium")(2AlCl_(3))+underset("Sulphate")underset("Barium")(3BaSO_(4))` |
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| 94. |
Why is epidermal peel generally taken from lower surface of the leaf ? |
| Answer» In dicot plants stomata are found in lower surface only, hence peel is taken from the lower surface. As stomata are present on both the surfaces of leaf in monocot plants so the peel can be taken from either surface. | |
| 95. |
What do you mean by biomagnification of harmful chemicals ? How does this phenomenon affect the human health ? |
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Answer» Biomagnification of harmful chemicals. Harmful chemicals enter through the soil and water in the first trophic level of the food chain and then their concentration goes on increasing in the second trophic level to the last trophic level. This incrasing concentration of toxic substances within each successive trophic level in the food chain is known as biomagnification of harmful chemicals. Human being is at the last trophic level of its food chain. So harmful chemicals enter into humans bodies in maximum quantity and thus damage our internal body organs and cause many types of diseases in our body. |
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| 96. |
1 g of solid sodium chloride is taken in a clean and dry test tube and 2 mL of conc. Suphuric acid is added to it . If the gas evolved is tested first with dry and then with wet blue litmus paper, in which case will the litmus paper change colour? Give reason for your answer. what inference can be drawn about the nature of the evolved gas ? Support your answer with a chemical equation for the reaction. |
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Answer» `2NaCl + H_(2)SO_(4)("conc.") to Na_(2)SO_(4) + 2HCl` Concentrated suphuic acid reacts with sodium chloride to form hydrogen chloride gas. When the gas evolved is tested with dry blue litmus paper then there is no change in the colour of the dry blue litmus paper. This shows that HCl gas does not behave as an acid in the absence of water. When the gas is tested with wet blue litmus paper then the blue litmus paper turns red. this shows that HCl gas shows acidic behaviour in the presence of water. Explanation : Dry HCl does not contain any hydrogen ions `(H^(+))` in it , so it does not show acidic behaviour so HCl gas does not change the colour of the dry of the dry blue litmus paper. When HCl gas it tested with wet blue litmus paper then HCl gas first dissolves in water to form HCl acid solution. ` HCl(g) overset("dissolves")underset(" in water")to HCl(aq)` ` HCl(aq) to H^(+)(aq) + Cl^(-)(aq)` HCl solution forms hydrogen ions which can turn blue litmus paper to red. ` Or, HCl + H_(2)O to H_(3)O^(+) + Cl^(-)` |
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| 97. |
(a) Write the name given to bases that are highly soluble in water. Give an example. (b) Why does bee using cause pain and irritation ? Rubbing of baking soda on the sting area gives relief. How ? |
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Answer» (a) Water soluble bases are called alkalis, e.g., NaOH, KOH. (b) Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. This can be prevented by clearing the mouth and teeth using tooth pastes which are generally basic and can neutralize the excess acid. (c ) Bee sting pain, a mild base like baking soda is rubbed on stung area as the mild base neutralizes the acid. |
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| 98. |
(i) Name two waste products which are stored in old xylem in plants. (ii) Name the process by which plants get rid of excess water. Name the pores through which this process takes place. |
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Answer» (i) Resin and gums are the two wastes which are stored in old xylem in plants. (ii) Transpiration is the process by which plants get rid of excess water. Stomatal pores are the pores through which transpiration takes place. |
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