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3251.

Sulphide ore is concentrated by which method?

Answer»

SOLUTION :FROTH FLOATATION
Discussion
3252.

Suggest two methods to reduce the effect of rancidity.

Answer»

Solution :To REDUCE the problem of rancidity - (1) Keep the FOOD in a CLOSED container. (2) USE antioxidants.
Discussion
3253.

Suggest a suitable method of preparation of the salts A, B, C and D (do not describe, give only balanced chemical equations). (i) A is a sodium salt. (ii) B is an insoluble salt. (iii) C is a soluble salt of copper. (iv) D is a soluble salt of zinc.

Answer»

Solution :(i) `2NaOH+H_(2)SO_(4)toNa_(2)SO_(4)+2H_(2)O`
(II) `Na_(2)SO_(4)+BaCl_(2)toBaSO_(4)+2NaCl`
(III) `CuO+H_(2)SO_(4)toCuSO_(4)+H_(2)O`
(iv) `Zn+H_(2)SO_(4)toZnSO_(4)+H_(2)`
Discussion
3254.

Suggest a reason for each oberservation given below. (i)In firework ,powedered magnesium is used rather than 'magnesium ribbon. (ii)Zinc and dilute H_(2)SO_(4) react much more quickly when a few drops of copper sulphate solutions are added. (iii)Zinc and dilute H_(2)SO_(4) react much more quickly when a few drops of copper sulphate solutions are added. (iii)The reaction between magnesium carbonate and dilute hydrochloric acid speeds up when some concentrated HCl is added.

Answer»

Solution :(i)In FIRE works.powdered MAGNESIUM is used because it has more surface area than magnesioum ribbon.Because of more surface area,powdered magnesium reacts FASTER than magnesium ribbon.
(ii)Zinc and dilute `H_(2)SO_(4)` react much more quickly when a few drops of copper sulphate solution is added .Copper sulphate acts as a catalyst which increases the rate of the reaction.
(iii)When concentration of the REACTANTS increases ,the rate of the reaction also increases .So the reaction between magnesium carbonate and dilute hydrochloric acid speeds up by the ADDITION of some concentrated HCl.
Discussion
3255.

Suggest a methodother than sublimation by which the components of a mixture of sugar and camphor can be separated.

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SOLUTION :The mixture is poured in water in a beaker and stirred. Suggar GOES into the solution. Camphor is FILTERED out. The FILTRATE is evaporated to dryness to get BACK the sugar.
Discussion
3256.

Sugarcane requires…..soil

Answer»

Acidic
Alkaline
neutral
Amphoteric

Answer :A
Discussion
3257.

Sugandha prepares HCl gas in her school laboratory using certain chemicals, She puts both dry and wet blue litmus paper in contact with the gas. (i) Name the reagents used by Sugandha to prepare HCl gas. (ii) State the colour changes observed with the dry and wet blue litmus paper. Show the formation of ions when HCl gas combines with water.

Answer»

Solution :(i) Solid SODIUM chloride and conc. Sulphuric acid
(ii) Dry LITMUS- no change
Wet blue litmus- changes to RED
(III) `HCl+H_2O to H_3O^(+)+CL^-`
(Hydronium ion) (Chloride ion)
Discussion
3258.

Successive ionisation potentials of an element 'X' are IP_(1) = 520 kJ mol^(-1), IP^(2) = 7,298 kJ mol^(-1) and IP^(3) = 10,815 kJ mol^(-1) Give the probable formulae of chloride and oxide of 'X'.

Answer»

Solution :(i) COMPARING IP values, VALENCY of X
(ii) ABRUPT change in IP value
(III) valence electronic configuration of STABLE ion
(iv) valencise of the corresponding postive and
negative radicals
Discussion
3259.

Substitution of hydrogen of methane by chlorine in the presence of sunlight forms ...........

Answer»

SOLUTION :`CH_(3)CL`
Discussion
3260.

Substances that are capable of adding oxygen to others are called _____ agents.

Answer»

SOLUTION :OXIDISING
Discussion
3261.

Sub atomic particles of atoms are

Answer»

protons
electrons
NEUTRONS
all of these

Solution :all of these
Discussion
3262.

Study the table in which the levels of Thyroid Stimulting Houmone (TSH) in women are given and answer questions on the basis of your understanding of the following paragraph and the related studied concepts. Women are at greater risk for developing abnormal TSH levels during menstruation,while giving birth and after going through menopause. Around 5% of women in the United Stateshave some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules. Q. A 35 year old woman has TSH level 6.03 mU/L. What change she bring in her diet to control this level?

Answer»

Solution :For a 35 year OLD, TSH 6.03 mU/L is higher than NORMAL. A high TSH indicates that thyroid is FUNCTIONING less than normal, hence she should INCLUDE more iodine or sea-food in her diet.
Discussion
3263.

Study the variation in the atomic radii of first group elements given below and arrange them in an increasing order. Group I elements : Na Li Rb Cs K Atomic radius (pm): 186 152 244 262 231

Answer»

Solution :Increasing order of the atomic radii :
Group I elements : `LiltNaltKltRbltCs` Atomic radius (pm) : 152 186 231 244 262
Discussion
3264.

Study the table in which the levels of Thyroid Stimulting Houmone (TSH) in women are given and answer questions on the basis of your understanding of the following paragraph and the related studied concepts. Women are at greater risk for developing abnormal TSH levels during menstruation,while giving birth and after going through menopause. Around 5% of women in the United Stateshave some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules. Q. Name the mineral that is responsible for synthesis of hormone secreted by thyoid gland.

Answer»

Solution :IODINE is RESPONSIBLE for synthesis of THYROXINE by THYROID GLAND.
Discussion
3265.

Study the table in which the levels of Thyroid Stimulting Houmone (TSH) in women are given and answer questions on the basis of your understanding of the following paragraph and the related studied concepts. Women are at greater risk for developing abnormal TSH levels during menstruation,while giving birth and after going through menopause. Around 5% of women in the United Stateshave some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules. Q. State the consequence of low TSH level.

Answer»

Solution :Low TSH INDICATES high function of thyroid gland which may RESULT in hyperthyroidism i.e.,INCREASED BMR.
Discussion
3266.

Study the table in which the levels of Thyroid Stimulting Houmone (TSH) in women are given and answer questions on the basis of your understanding of the following paragraph and the related studied concepts. Women are at greater risk for developing abnormal TSH levels during menstruation,while giving birth and after going through menopause. Around 5% of women in the United Stateshave some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules. Q. When do women face a greater risk of abnormal TSH level?

Answer»

SOLUTION :WOMEN face greaterrisk of ABNORMAL TSH level during MENSTRUATION, PREGNANCY and after menopause.
Discussion
3267.

Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the modern periodic table : On the basis of the above table, answer the following questions : (i) Name the element which forms only covalent compounds. (ii) Name the element which is a metal with valency three. (iii) Name the element which is a non-metal with valency three. (iv) Out of D and E, which is bigger is size and why ? (v) Write the common name for the family to which the elements C and F belong.

Answer»

Solution :(i) Element E will form covalent COMPOUNDS by sharing its four VALENCE ELECTRONS.
(ii) Element D is a METAL with valency three.
(iii) Element B is a non-metal with valency three.
(iv) We know that the size of elements decreases on moving left to right in a period. Therefore, element D is GREATER than element E.
(v) The name of the family to which elements C and F belong is the noble gas family (group 18).
Discussion
3268.

Study the given diagram and answer the following questions : (a) Write the chemical reaction involved in the process. (b) Mention the colour of : (i) Copper powder and (ii) the substance formed after heating it. (c) How can we reverse the above reaction ? Write the equation for the reverse reaction and state the substance that under-goes oxidation and the substance that undergoes reduction.

Answer»

Solution :(a) Copper powder upon heating reacts with oxygen(present in air) to form cupric oxide or copper (II) oxide.
`2Cu(s) + O_(2)(g) overset("HEAT")to underset("Cupric oxide")(2CuO(s))`
(b) )(i) Copper powder is BROWNISH in colour.
(ii) The substance formed after heating is cupric oxide. It has black colour.
(C) The reaction can be reversed by heating cupric oxide in a CURRENT of hydrogen.
`CuO(s) + H_(2)(g) to Cu(s) + H_(2)O(g)`
In this reaction, `H_(2)` undergoes oxidation to `H_(2)O` and CuO is reduced to Cu.
Discussion
3269.

Study the data of the following three categories A, B and C. (i) from the given three categories A, B and C, pick the one which forms Dobereiner.s Triads. (ii) Why did Mendeleev placed elements of category A, B and C in three different groups? (iii) Is Newland law of octaves applicable to all the three categories? Give reason to justify your answer.

Answer»

Solution :(i) Category A forms triad, `(7+39)//2=23.`
(ii) Mendeleev based his periodic table on the law that properties of elements are periodic function of atomic MASSES.
He sorted out the elements with similar properties and grouped them together. Li, Na and K has similar properties, they were grouped together. N, P and As had similar properties they were grouped together. Similarly, B, Al and Ga has similar properties, they were grouped together.
(iii) Newlands law of OCTAVES was APPLICABLE upto calcium. After calcium, every eighthelement did not have properties similar to the first. Therefore we can say that elements of category A FOLLOWS Newlands law.
Discussion
3270.

Structure of the Modem Periodic table.

Answer»

Solution :(i) The Modem Periodic table CONTAINS seven horizontal rows called the periods 1 to 7.
(II) SIMILARLY, eighteen vertical columns are the groups 1 to 18.
(iii) The arrangement of the periods and groups results into formation of boxes.
(iv) Atomic numbers are serially indicated in the upper part of these boxes.
(v) Each box corresponds to the place for one element.
(vi) Apart from these seven rows, two separate rows are placed at the bottom of the periodic table.
(vii) These are called Lanthanide series and Actinide series respectively.
(viii) There are 118 boxes in the periodic table including the two series.
(ix) It means that there are 118 places for elements in the Modem Periodic table.
(x) The Modem Periodic table is now completely filled, means all the 118 elements are now discovered.
(xi) The entire periodic table is divided into FOUR blocks, viz, s-block, p-block, d-block and £-block.
(XII) The s-block contains the groups 1 and 2 elements.
(xiii) The groups 13 to 18 constitute the p-block elements.
(xiv) The groups 3 to 12 constitute the d-block elements. The d-block elements are called transition elements.
(xv) The lanthanide and actinide series at the bottom form the £-block elements.
(xvi) A zig-zag line can be drawn in the p-block of the periodic table. (xvii) The metalloid elements lie along the border of the zig-zag line.
(xviii)All the metals lie on the left side of the zig-zag line, while all the non-metals lie on the right side.
Discussion
3271.

Structure of cyclobutane is………………..

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ANSWER :A
Discussion
3272.

Structural formula of ethyne is …

Answer»

`H-C-=C-H`
`H_(3)C-C-=CH`

ANSWER :A
Discussion
3273.

Strongest salt amongst the following is

Answer»

`NaCl`
`CaCl_(2)`
`BaSO_(4)`
`LiCl`

Solution :NA
Discussion
3274.

Strength of a solution is given by

Answer»

`("MASS of the solute in grams ) / (Volume of SOLUTION in litres")`
`("Mass of the solvent in grams ) / (Volume of solution in litres")`
`("Mass of the solute in KILOGRAMS ) / (Volume of solution in litres")`
NONE of the above

Answer :A
Discussion
3275.

STPmeans ________.

Answer»

SOLUTION :STANDARD TEMPERATURE and PRESSURE
Discussion
3276.

Stinging hair of nettle leaves inject ethanoic acid and cause pain.

Answer»

SOLUTION : FALSE – It is methanoic ACID not ETHANOIC acid.
Discussion
3277.

Steel manufactured using the open hearth process is of better quality compared to steel maunfactured by Bessemer process and L-D converter. Give reasons.

Answer»

Solution :Open HEARTH process produces better quality STEEL because
(i) Open hearth process is a lengthy process due to which the composition of the product can be controlled by checking from time to time.
(ii) As blast ot air is not passed in the open hearth process, blow are not formed that could MAKE the steel brittle and LOSS of iron in the form of SLAG is multified.
(iii) Pure oxygen makes the process of removal of impurities faster and more effective.
Discussion
3278.

Steel is preferred over iron in construction of ships because

Answer»

melting point of STEEL is higher than IRON
steel is more uniform than Iron
steel does not RUST
tensile strength of steel is not high

ANSWER :C
Discussion
3279.

State what happens whn ethanoic acid reacts with sodium.

Answer»

Solution :Ethanoic ACID REACTS with sodium metal to evolve hydrogen gas.
`2CH_(3)COOH + UNDERSET("sodium") rarr underset("Sod. Acetate")(2CH_(3)COONA) + H_(2)`
Discussion
3280.

State what happens when zinc granules are heated with sodium hydroxide solution. Write the balanced chemical equation for the reaction. Name the main product formed for the this reaction .

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Solution :When zinc granules heated with NaOH solution, sodium ZINCATE is formed with the evolution ofhydrogen gas .
`2NaOH(AQ)+Zn(s) overset ("Heat")rarrNa_(2)ZnO_(2)(aq)+H_(2)G`
THEA main product formed in this reaction is `H_(2)` gas.
Discussion
3281.

State what happens when : (a) Gypsum is heated at 373 K (b) Blue crystals of copper sulphate are heated (c ) Excess of CO_(2) is passed through lime water.

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Solution :It turns into PLASTER of PARIS `(CaSO_(4). ½H_(2)O)` by losing water MOLECULES.
(b) It LOSES its CRYSTALLINE structure and the characteristic blue colour and turns into a while powder.
(c ) The lime water first turns milky due to the formation of the insoluble Calcium carbonate. But with excess of the gas being passed it forms the soluble Calcium bicarbonate and the milky appearance disappears.
Discussion
3282.

State two ways to prevent the rusting of iron.

Answer»

Solution :The rusting can be PREVENTED by
(1) By painting, oiling, greasing, galvanising, chrome PLATE or anodising.
(2) By FORMING alloys.
Discussion
3283.

State two properties of each of the following metals which make them suitable for :(i) Copper and aluminium for making electric wires. (ii) Gold, platinum and silver are used to make jewellery. (iii) Copper to make hot water tank.

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Solution : (i) Copper and aluminium are ductile and good conductors of ELECTRICITY.(II) Gold, platinum and silver are MALLEABLE and ductile. (III) Copper is malleable and good conductor of heat.
Discussion
3284.

State two reasons for rejecting law of octaves.

Answer»

Solution :1. This law did not extend properly beyond the element CALCIUM
2. This law did not provide for any specific PLACE for HYDROGEN.
Discussion
3285.

State two physical properties of gold which are of extreme use to jewellers.

Answer»

SOLUTION :MALLEABILITY, DUCTILITY, LUSTROUS.
Discussion
3286.

State two main properties of elements on which Mendeleev's periodic classification was based. Why position of hydrogen is not fixed in his periodic table ?

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Solution :(i) Physical properties of elements are periodic function of their ATOMIC masses.
(ii) Similar formula of OXIDES and HYDRIDES formed by elements of same GROUP was selected as chemical property as basis of classification.
The atomic number of hydrogen is 1. Hence, it should occupy the first position in group 1 of the periodic table. But because of its chemical similarity with elements of group 1 and 17, the position of hydrogen in the periodic table is not fixed.
Discussion
3287.

State two conditions necessary for rusting of iron.

Answer»

Solution :Conditions for rusting of iron :
(i) The PRESENCE of WATER and oxygen is ESSENTIAL for the rusting of iron.
(ii) Impurities in the iron, the presence of water vapour, acids, salts and carbon dioxide hastens rusting.
(iii) Pure iron does not dust in dry and `CO_(2)` free AIR. It also does not rust in pure water, free from dissolved salts.
Discussion
3288.

State three reasons for the following facts: a. Sulphur is a non metal. b. Magnesium is a metal.

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Solution :(i) Sulphur is a non metal
1. Poor conductor of heat and ELECTRICITY
2. Neither MALLEABLE nor ductile
3. `S+O_(2)toSO_(2)`
`SO_(2)+H_(2)OtoH_(2)SO_(3)`
(Sulphurous acid)
Sulphurdioxide is acidic OXIDE
(ii) Magnesium is a metal
Good conductor of theat adn electricity. Maleable and ductile.
`2Mg+O_(2)to2MgO`
`MgO+H_(2)OtoMg(OH)_(2)`
(Magnesium hydroxide)
Magnesium oxide is BASIC in nature.
Discussion
3289.

State the valency of each carbon atoms in (1) an alkane (2) alkyne .

Answer»

Solution :(i) Valency of each CARBON ATOM in ALKANE is FOUR .
(ii) Valency of each carbon atom in alkyne is four.
Discussion
3290.

State the uses of ethanol.

Answer»

Solution :The uses of ETHANOL are as follows:
(1) It is used as an industrial solvent in medicines such as tincture iodine, cough syrups and many tonics.
( 2 ) It is used in the preparation of lacquers, VARNISHES and fragrant substances LIKE perfumes.
(3) It is used as an antiseptic.
( 4 ) PURE ethanol (absolute alcohol) is the active ingredient of all alcoholic drinks.
(5) It is used to prepare rectified spirit.
Discussion
3291.

State the type of reaction represented by the following equation: 2KClO_(3) overset("heat") to 2KCl +3O_(2)

Answer»

SOLUTION :THERMAL DECOMPOSITION.
Discussion
3292.

State the type of reactionin Vegetable matter changing into compost.

Answer»

Solution :Vegetable MATTER CHANGING into COMPOST is an exothermic and decomposition REACTION.
Discussion
3293.

State the type of reactionin Adding water to quick lime to form slaked lime.

Answer»

SOLUTION :ADDING water to quick lime to form slaked lime is combination REACTION, which is EXOTHERMIC.
Discussion
3294.

State the type of reactionin Burning of natural gas

Answer»

SOLUTION :BURNING of natural gas is an EXOTHERMIC REACTION.
Discussion
3295.

State the type of chemical reaction used for the extraction of metals from their naturally occuring chlorides or oxides.

Answer»

SOLUTION :ELECTROLYTIC REDUCTION.
Discussion
3296.

State the true and false option for the chemical reaction given below: 3Fe(s)+4H_(2)O(g) to Fe_(3)O_(4) to FeO_(4)(s)+4H_(2)(g)(i) Fe is being oxidised. (ii) Water is being reduced. (iii) Water acts as reducing agent. (iv) Water acts as oxidising agent.

Answer»

SOLUTION :Here. (i), (II) and (iv) are TRUE options, while (III) is a false OPTION.
Discussion
3297.

State the similarity in the electronic configuration of all the elements present in group 1 of the periodic table.

Answer»

Solution :Elements in a GROUP have SIMILAR ELECTRONIC configuration so all of them have 1 valence ELECTRON.
Discussion
3298.

State the role played by the following in the process of digestion. (i)Enzyme trypsin (ii) Enzyme lipase

Answer»

Solution :(i) ENZYME Tryspin : It is frleased by pancreas in the small INTESTINE.
Proteoses and dipeptides `OVERSET("Trypsin")to ` Peptides.
(II) Enzyme Lipase : Released by opancreas in small intestine.
Emulsified FATS `overset("Lipase")to` Diglycerides.
Discussion
3299.

State the reason why (i) carbon is not used to reduce the oxides of sodium or aluminium. (ii) an iron strip dipped in a blue copper sulphate solution turns the blue solution to pale green. (iii) calcium does not occur in free state in nature. (iv) zinc is used in the galvanisation of iron and not copper.

Answer»

Solution :(i) Both sodium and ALUMINIUM are stronger REDUCING agents than carbon. Therefore, carbon is not in a POSITION to reduce the oxides of these metals to the metallic form.
(b) Iron displaces copper from copper sulphate solution to form iron sulphate which imparts PALE green colour to it.
(iii) Calcium (Ca) is a reactive metal and is placed high in the activity series. It therefore, does not exist in free state also called native state.
(iv) Zinc is placed above iron in the activity series. When deposited over its surface (galvanisation), zinc gets corroded and not iron. But copper is placed below iron and therefore, does not participate the CORROSION. In this case, iron is corroded or rusted.
Discussion
3300.

State the reason why carbon forms a covalent compound and notC^(4+) and C^(-4). Also give reasons why covalent compounds are bad conductors of electricity and have law melting and low boiling points.

Answer»

Solution :ATOMIC number of carbon is SIX. This means that it has four electrons in its outermost shell and it needs four more electrons to attain noble gas electronic configuration. It does not form `C^(+4)` cation, as the removal of four valence electrons will require a huge amount of energy. The cation formed will have six protons and two electrons. This makes it highly UNSTABLE. Carbon is unable to form `C^(-4)` anion as its nucleus with six protons will not be able to hold ten electrons. Thus, carbon achieves noble gas electronic configuration by sharing its four electrons with other ELEMENTS, i.e. it forms covalent compounds.
(i) Covalent compounds are bad conductors of electricity due to lack of free electrons.
(ii) Covalent compounds are formed by covalent bonds and it has been found that the intermolecular forces of attraction in covalent compounds are weak. Thus, their MELTING and boiling points are quite low.
Discussion