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901.

Which of the following always decreases down a group?

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METALLIC character
Non-metallic character
CHEMICAL reactivity
ATOMIC size 

Answer :B
Discussion
902.

Which of the following belong to the same homologous series? C_(3)C_(8),C_(4)H_(8),C_(3)H_(6)

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ANSWER :`C_(4)C_(8),C_(3)H_(6).`
Discussion
903.

What is 'baking powder' ? How does it make the cake soft and spongy ?

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Solution :Baking powder is a mixture of baking soda `(NaHCO_3)` and an edible ACID LIKE tartaric acid.
Baking powder on heating produces carbon dioxide gas which CAUSES break or cake to rise making it soft and spongy.
`UNDERSET("Baking soda")underset("HYDROGENCARBONATE")underset("Sodium")(NaHCO_3)+underset("From tartaric acid")(H^(+))overset("Heat")rarrCO_(2)+H_(2)O+` Sodium salf of tartaric acid
Discussion
904.

The valency of all alkali metals is one

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SOLUTION :N/A
Discussion
905.

What is pH scale ?

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Solution :PH scale is that scale which indicates WHETHER the given solution is ACIDIC, basic or neutral. On this scale, pH values of VARIOUS solution lie between 0 to 14.
Discussion
906.

What is the role of a catalyst in a chemical reaction?

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Solution :Catalyst changes (USUALLY increases but sometimes DECREASES) the RATE of a chemical REACTION without itself being CONSUMED in the reaction.
Discussion
907.

Use of CFC free refrigerators is considered as eco friendly. Why?

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Solution :This is because chlorofluoro CARBON coming out from air conditioner and refrigerator has led to the depletion of OZONE layer which PROTECTS us from UV rays which can cause many harmful diseases like SKIN cancer, loss of eyesight etc.
Discussion
908.

What is the condition of an electromagnetic induction

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There must be a RELATIVE motion between the COIL of WIRE and GALVANOMETER
There must be a relative motion between the galvanometer and a magnet
There must be a relative motion between galvanometer and generator
There must be a relative motion between the coil of wire and a magnet

SOLUTION :There must be a relative motion between the coil of wire and a magnet
Discussion
909.

The rust has the chemical formula as Fe_(3)O_(4)

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Solution :The RUST has the CHEMICAL formula as `Fe_(2)O_(3) . xH_(2)O`.
Discussion
910.

What would be the structure of ethanoic acid which had the formula CH_3COOH

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SOLUTION :
Discussion
911.

Why alloys are said to solid solutions?

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Solution :ALLOYS can be considered SOLID solutions in which the metal with high concentration is solvent and other metals are SOLUTE.
For EXAMPLE, BRASS is a solid solution of zinc (solute) in copper (solvent).
Discussion
912.

Which of the following always increases down a group?

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METALLIC CHARACTER
Non-metallic character
Electronegativity
ACIDIC nature of OXIDES 

Answer :A
Discussion
913.

What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes?

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Solution :Iron nails become BROWNISH in colour and the blue colour of COPPER sulphate solution fades. This is because iron DISPLACES copper from copper sulphate solution and forms FERROUS sulphate which is COLOURLESS.
Discussion
914.

Write the chemical equation of the reaction which takes place on burning ethanol in oxygen.

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SOLUTION :`C_2H_5OH + 3O_2 to 2CO_2+ 3H_2O + ` HEAT
Discussion
915.

What do you mean by Electro negativity?

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Solution :Electro negativity is RELATIVE tendency of a bonded atom to attract the bond-electrons towards it. It just compares the tendency of various elements to attract the bond-electrons towards themselves.
(a) Electron negativity decreases in a GROUP from top to bottom
(b) Electron negativity increases in a period from left to RIGHT
(c) Electro negativity is related to ionizatio energy. Electrons with low ionization energies have low electro negativity because their nuclei do nto exert a strong attractive force on electrons.
(d) Elements with high ionization energies have high electro negativity due to the strong PULL exerted on electrons by the NUCLEUS.
Discussion
916.

What are addition reaction? What are catalysts? Illustrate with an example.

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Solution :Reactions which involve addition of two reactants to form a single product aren called addition reactions. Catalysts are the substanceswhich can change, usually increase the SPEED of a chemical reaction without being USED up in that reaction.
For example, vegetable oils having LONG unsaturated carbon chains are converted into vegetable ghee by HEATING them in presence of Nickel, platinum or palladium metals used as catalysts.
`underset("(LIQUID)")("Vegetable oil"+ H_2) overset("Nickel 48 K")to underset("Solid")("Vegetable Ghee")`
Discussion
917.

Why C_(2)H_(2) can't exits?

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SOLUTION :There are too MANY hydrogen ATOMS for TWO carbon atoms.
Discussion
918.

What are ionic or electrovalent compounds? Give an example of ionic compound . Explain with reason four properties of these compounds.

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Solution :Ionic compounds are those compounds which are formed by the TRANSFER of electrons from a metal to a non metal For example `NaCl.`
PROPERTIES:
(i) Physical nature: Ionic compounds are hard and solid due to strong force of attraction between oppositely charged ions.
(ii) Melting point and boiling point: As more amount of energy is required to break strong bonds. So they arehigh melting point and boiling point
(iii) Solubility: These are soluble in WATER (polar SOLVENT) but insoluble in ORGANIC solvent.
(iv) Conduction of electricity: They conduct electricity in solution or molten state as ions move towards opposite electrodes.
Discussion
919.

While performing a reaction between Zinc and Sulphuric acid, which gas is evolved

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CARBON dioxide
Hydrogen
Nitrogen
Oxygen

Answer :B
Discussion
920.

Which one of the following processes involve chemical reactions ?

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Storing of oxygen gas under pressure in a gas cylinder.
Liquefaction of air.
Keeping petrol in a chine dish in the open.
HEATING COPPER wire in presence of air at high temperature.

Solution :Copper wire on heating in presence of air at high temperature forms copper oxide, which is a CHEMICAL REACTION. Processes in (a), (b) and (c) do not INVOLVE any chemical change.
Discussion
921.

What should be done to avoid the misuse of ethanol for drinking purpose ?

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Solution :Ethanol is an important industrial solvent.
To prevent the MISUSE of ethanol produced for industrial use, it is made unfit for DRINKING by ADDING poisonous substances like methanol, pyridine to it.
Discussion
922.

What is the change in pH values of milk when it changs into curd? Explain.

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SOLUTION :PH decreases
It is due to the FORMATION of lactic acid in curd. Since, acids generally have a low pH value, so when milk changes to curd its pH will decreases.
Discussion
923.

Write the physical properties of ethanoic acid.

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Solution :The physical properties of ethanoic acid (acetic acid) are as follows:
(1) Ethanoic acid is a colourless LIQUID having vinegar like odour.
(2) The boiling point of pure ethanoic acid is 391 K.
(3) The melting point of pure ethanoic acid is 290 K and hence it often FREEZES during winter in cold climates. Therefore, it is also known as glacial acetic acid.
(4) 5 - 8 % solution of ethanoic acid in WATER (aqueous solution) is CALLED vinegar.
(5) Ethanoic acid is a weak acid, but hydrochloric acid is a strong acid as it ionises completely.
Discussion
924.

What would you observe when zinc is added to a solution of iron(II) sulphate ? Write the chemical reaction that takes place

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SOLUTION :As zinc is more reactive than iron, displacement reaction will take PLACE.
`underset("Iron(II) SULPHATE ")(Zn(s) + FeSO_4(aq)) to underset(" Zinc sulphate")(ZnSO_4 (aq)+ Fe(s))`
Discussion
925.

Write the number of elements present in first, third and fourth period in the modern periodic table.

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ANSWER :2, 8, 18
Discussion
926.

Why are metals electropositive and non-metals electronegative in nature? Illustrate by giving an example of each. Why does metallic character of elements increase down a group?

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Solution :a] Metals have 1-3 valence electrons and hence they tend to lose electrons to attain noble gas configuration. For example, Sodium is a metal which has | valence electron. It can easily lose this valence electron rather than GAIN 7 more electrons to attain a noble gas configuration while forming compounds. Hence, metals are electropositive in nature. Non-metals have 5-8 valence electrons (except Carbon which has 4 valence electrons). It is easier for them to gain electrons to acquire noble gas configuration and hence they are ELECTRONEGATIVE. Example: Nitrogen is a non-metal with 5 valence electrons which GAINS 3 electrons during bonding. Hence, it is electronegative.
b] Down a group, the number of electron shells increases and hence the distance between valence electrons and nucleus increases. The attractive FORCE between them goes on reducing thereby making it easier to lose electrons. This increases electropositivity and hence the metallic character.
Discussion
927.

What is obtained by the combustion of methane?

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SOLUTION :`CO_(2)` and `H_(2)O`
Discussion
928.

Which of the following is th best electrical conductor?

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GOLD
Silver
Copper
Aluminium

Answer :B
Discussion
929.

Two coloured salt solution of two metals A and B gave precipitates with NaOH and NH_(4)OH. On further additions of NH_(4)OH, the precipitate disappears, in the case of B. There is no such change in the case of 'A' either with NaOH or NH_(4)OH. Identify A and B. Give equations

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Solution :(i) metals GIVING coloured salts
(ii) coloured salts that GIVEN precipitates with NaOH and `NH_(4)OH`
(III) COMPARISON between the reactions of the precipitates obtained with excess NaOH and `NH_(4)OH`
(iv) solubility of the product FORMED
Discussion
930.

When a drop of orange juice is added to pure water, how the pH value will vary for water? If a drop of lemon juice is also added, will there be any more change in the pH value.

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SOLUTION :ORANGE and lemon are CITRUS fruits which contain citric acid in their juices.
When these juices are added to pure water, the acid will release `H^+` ions on dissociation and the pH value will decrease from 7 as the acidity INCREASES.
Discussion
931.

Which of the following is (are) true when HCl (g) is passed through water ? (i) It does not ionise in the solution as it is a covalent compound. (ii) It ionises in the solution. (iii) It gives both hydrogen and hydroxyl ion in the solution. (iv) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule

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(i) only
(iii) only
(ii) and (IV)
(iii) and (iv)

Solution :Although HCl is a covalent compound but it IONISES in the solution. `H^+` COMBINES with WATER to give hydronium ion.
Discussion
932.

What would happen if you add zinc coated iron nail into the solution of copper sulphate ? Give reason for your prediction.

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Solution :The zinc COATED iron nail will react with the `CuSO_(4)` and the blue COLOUR of the solution gradually fade and after SOMETIME solution will turn GREEN because, now, iron nail will react with the copper sulphate. This happens because iron and zinc both displace the copper of copper sulphate solution because iron and zinc both are more reactive than copper.
Discussion
933.

The standard reduction potentials of three metals cations X, Y and Z are + 0.52, – 3.03 and – 1.18 V respectively. Arrange X, Y and Z in order of increasing reducing power

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ANSWER :`X LT Z lt Y`
Discussion
934.

Which of the following are isomers of butane ?

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`H-UNDERSET(H)underset(|)OVERSET(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-H`


ANSWER :A::B
Discussion
935.

What happens when a liquid boils ?

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SOLUTION :During boiling , a LIQUID gets TRANSFORMED into its VAPOUR.
Discussion
936.

Which of the following is strong acid.

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ACETIC acid
Nitric acid
Citric acid
Oxalic acid

Answer :B
Discussion
937.

Which one of the following is a home diatomic molecule?

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`H_(2)`
`CO`
`NO`
`O_(3)`

SOLUTION :`H_(2)`
Discussion
938.

Which of the statements about the reaction below are incorrect ? 2PbO(s)+C(s)to2Pb(s)+CO_(2)(g) Carbon is getting oxidised.

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SOLUTION :CARBON is GETTING oxidised is CORRECT ANSWER.
Discussion
939.

What is the maximum number of electrons that can be accommodated in a shell? Write the formula.

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SOLUTION :
Discussion
940.

Write the chemical formula for washing soda. How may it be obtained from baking soda ? Name an industrial use of washing soda other than washing clothes.

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SOLUTION :`Na_2CO_3 . 10H_2O`
BAKING soda `(NaHCO_3)` on HEATING produces SODIUM carbonate `(Na_2CO_3)` which on recrystallisation produces washing soda
`2NaHCO_3 overset(Delta)to Na_2CO_3 + H_2O + CO_2 uarr`
`Na_2CO_3 + 10H_2O overset("Crystallisation")to Na_2CO_3 . 10H_2O`
Washing soda is used in the MANUFACTURE of glass.
Discussion
941.

Which of the following species cannot have conjugate base ?

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`HSO_(4)^(-1)`
`HPO_(4)^(-2)`
`PO_(4)^(-3)`
`H_(2)PO_(2)^(-)`

Solution :`PO_(4)^(-3)` has only conjugate acid, that is `HPO_(4)^(-2)`. It has no conjugate base as it does not possess any replaceable `H^(+)` ION
Discussion
942.

What is structural isomerism? Draw isomers of pentane.

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Solution :Structural ISOMERISM is a form of isomerism in which molecules with the same molecular formula have DIFFERENT bonding pattern and atomic organisation.
Isomers of Pentane:
n - Pentane`H-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-H`
ISO - Pentane `H-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)overset(-C-)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-H`
Neo Pentane`H-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)underset(H-C-H)underset(|)overset(H)overset(|)overset(-C-)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-H`
Discussion
943.

X, Y and Z are the elements of a Dobereiner's Triad. If the atomic mass of X is 7 and that of Z is 39, what should be the atomic mass of Y?

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Solution :Atomic MASS of X = 7
Atomic mass of Z = 39
`:. ` ACCORDING to Dobereiner.s Triad, atomic mass of Y
`=(X+Z)/2=(7 + 39)/2=46/2 =23`
`:.`Atomic mass of Y = 23
Discussion
944.

Three elements X, Y and Z belong to 17^(th) group but 2^(nd),3^(rd)and4^(th) period respectively. Number of valence electrons in Y is 7. Find the number ofvalence electrons in X and Z.

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Solution :It will be 7 in X as well as in Z.
The REASON being that NUMBER of electrons in the OUTERMOST shell in the elements in same group is same.
Discussion
945.

Which of the following is not a thermodynamical function

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GIBBS FREE energy
Enthaply
Entropy
Work

Answer :D
Discussion
946.

Write the name and formula of the 2nd member of homologous series having general formula C_(n)H_(2n-2).

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Solution :The 2ND member is PROPENE, `C_(3)H_(4)`.
Discussion
947.

Write the name and formula of the 2nd member of homologousserieshaving general formula C_(n)H_(2n+2).

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Solution :The second MEMBER is ethane, `C_(2)H_(6)`.
Discussion
948.

Write the structural formula and IUPAC name of the following i) A carboxylic acid with 4 carbon atoms ii) An alkyne with three carbon atoms iii) An alcohol having one carbon atom

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SOLUTION :i] `CH_3-CH_2-CH_2-COOH`
`H-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-overset(O)overset(||)(C )-OH "Butanoic acid "`
ii] `CH_3-C=CH ""H-underset(H)underset(|)overset(H)overset(|)(C )-underset(H)underset(|)overset(H)overset(|)(C )-C-= C-H "PROPYNE"`
III] `CH_3-OH ""H-underset(H)underset(|)overset(H)overset(|)(C )-OH "Methanol"`
Discussion
949.

Write the IUPAC name of the compound having the formula CH_3-CH=CH-CH_3 .

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Solution : There are four C ATOMS in the chain involving double bond, THEREFORE, the root WORD is .but.. There is a double bond between carbon 2 and 3 in the chain, therefore, the primary SUFFIX is 2-ene.
Thus, the IUPAC name of the GIVEN compound is
Root word + Primary suffix
But + 2-ene = But-2-ene
Discussion
950.

When copper vessels are kept in open air, over a period of time they coated with a green layer. The green layer is

Answer»

COPPER OXIDE
copper SULPHIDE
copper sulphate
copper CHLORIDE

Answer :A
Discussion