Subject

Chemistry

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

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11.

Give reasons:
(i)Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows the highest oxidation state of +4.
(ii)Transition metals show variable oxidation states.
(iii)Actinoids show irregularities in their electronic configurations.


(i) Mn shows the highest oxidation state of +7 with oxygen because it can form p-pi−d-pi multiple bonds using 2p orbital of oxygen and 3d orbital of Mn. On the other hand, Mn shows the highest oxidation state of +4 with fluorine because it can form a single bond only.

ii) Transition metals show variable oxidation states due to the participation of ns and (n-1)d- electrons in bonding. Lower oxidation state is exhibited when the ns- electrons take part in bonding and higher oxidation states are exhibited when the (n-1) d-electrons take part in bonding.

(iii)Actinoids show irregularities in their electronic configurations because the energy differences between 5f, 6d and 7s subshells are very small. hence, an electron can be occupied in any of the subshells. They have the electronic configuration of 7s2 with a variation of occupancy in 5f and 6d orbitals.

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12.

(i) Name the method of refining of metals such as Germanium.
(ii)In the extraction of Al, impure Al2O3 is dissolved in conc. NaOH to form sodium aluminate and leaving impurities behind. What is the name of this process?
(iii)What is the role of coke in the extraction of iron from its oxides?

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13.

Calculate e.m.f of the following cell at 298 K:

2 Cr space left parenthesis straight s right parenthesis space plus 3 Fe to the power of 2 plus end exponent space left parenthesis 0.1 space straight M right parenthesis space rightwards arrow space 2 Cr to the power of 3 plus end exponent space left parenthesis 0.01 space straight M right parenthesis space plus 3 Fe left parenthesis straight s right parenthesis space

Given colon space straight E to the power of 0 space left parenthesis Cr to the power of 3 plus end exponent vertical line Cr right parenthesis space equals space minus 0.70 space straight V
space space space space space space space space space space space straight E to the power of 0 space left parenthesis Fe to the power of 2 plus end exponent vertical line Fe right parenthesis space equals negative 0.44 space straight V

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14.

(a) For the complex [Fe(CN)6]3–, write the hybridization type, magnetic character and spin nature of the complex. (At. number : Fe = 26).
(b) Draw one of the geometrical isomers of the complex [Pt(en)2Cl2]2+ which is optically active.

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15.

Out of  and which is more reactive towards
SN 1 reaction and why?

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16.

Write the IUPAC name of the given compound:

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17.

Write the mechanism of following chemical reaction:
2 CH subscript 3 CH subscript 2 OH space rightwards arrow from 413 straight k to Conc. space straight H subscript 2 SO subscript 4 of space CH subscript 3 minus CH subscript 2 minus straight O minus CH subscript 2 minus CH subscript 3

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18.

Given reasons:
(i)C–Cl bond length in chlorobenzene is shorter than C–Cl bond length in CH3–Cl.
(ii)The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
(iii)SN1 reactions are accompanied by racemization in optically active alkyl halides.

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19.

Write the main product(s) in each of the following reactions: 

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20.

(i) Write the name of two monosaccharides obtained on hydrolysis of lactose sugar.

(ii) Why Vitamin C cannot be stored in our body?

(iii) What is the difference between a nucleoside and nucleotide?

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