ISC Board Class 12 Chemistry Sample Exam 2025: Download Free PDF Here

Question 1

(A)

Fill in the gaps by selecting the appropriate word(s) from the brackets:

(four, three, remains the same, propane, ns1-2, increases, six, propan-2-ol, (n-1)d1-10, two, decreases, Clemmensen, Wolff-Kishner)

(4×1)

(I)

The molar conductance of a solution when diluted, but the specific conductance of a solution when diluted.

(Understanding)

(iii)

In the complex ion (CoCl(en)2ONO)+ the coordination number and the oxidation number of the central metal ion and (Understanding)

(iii)

Propanone is formed by reacting with zinc amalgam in the presence of concentrated HCl and the reaction is called reduction. (Reminder)

(iv)

The variation and extent of oxidation state in coordination complexes is due to the involvement of inner electrons in addition to outer electrons. (Understanding)

(B)

Select the correct alternative from the options given below and write it.

(7×1)

(I)

The correct order of increasing basicity of ammonia, methylamine and aniline is: (Analysis)

(A)

Methylamine

(B)

aniline

(C)

ammonia

(D)

aniline

(iii)

Colligative properties of a solution are: (understanding)

(P)

Regardless of the nature of the dissolved substance

(Q)

Proportional to the molecular mass of the solute

(R)

Proportional to the concentration of the dissolved substance

(S)

Regardless of the amount of solvent

(A)

Only P and Q are correct

(B)

Only P and R are correct

(C)

Only P and S are correct

(D)

Only Q and S are correct

(iii)

According to Markovnikov’s rule, “the negative part of the halogen acid binds to the C atom of an asymmetric alkene that has the smallest number of H atoms.”

Anti-Markovnikov addition of HBr is NOT observed in: (analysis)

(A)

Propen

(B)

But-2-en

(C)

But-1-en

(D)

Pent-2-en

(iv)

Most naturally occurring α-amino acids are optically active and have an L-configuration. Which of the following amino acids is NOT asymmetric?

(Retrieve)

(A)

Valine

(B)

Alanine

(C)

Glycine

(D)

Leucin

(v)

Which of the following complex ions has geometric isomers?

(Understanding)

(A)

(Ni(NH3)5Br)+

(B)

(Cr(NH3)4en)3+

(C)

(Co(NH3)2(en)2)3+

(D)

(Co(NH3)6)3+

from (vi)

Below are two statements labelled ‘Claim’ and ‘Reason’. Read the two statements carefully and select the correct option.

Claim: Tertiary butyl bromide undergoes a Wurtz reaction to form 2,2,3,3-tetramethylbutane.

Reason: In the Wurtz reaction, the same alkyl halides react with sodium in dry ether to form hydrocarbons. The resulting hydrocarbon contains twice the number of carbon atoms as the alkyl halide.

(Analysis)

(A)

Both the claim and the reason are true and the reason is the correct explanation of the claim.

(B)

Both the claim and the reason are true, but the reason is not the correct explanation for the claim.

(C)

The claim is true, but the reasoning is wrong.

(D)

Both the claim and the reason are false.

(vii)

Below are two statements labelled ‘Claim’ and ‘Reason’. Read the two statements carefully and select the correct option.

Claim: Lanthanides exhibit a continuous increase in size with increasing atomic number.

Reason: Lanthanides do not show lanthanide contraction. (Analysis)

(A)

Both the claim and the reason are true and the reason is the correct explanation of the claim.

(B)

Both the claim and the reason are true, but the reason is not the correct explanation for the claim.

(C)

The claim is true, but the reasoning is wrong.

(D)

Both the claim and the reason are false.

(C)

Read the text carefully and answer the questions that follow.

(3×1)

A plant or other living thing maintains an appropriate balance of C-14 (radioactive carbon) in its tissues throughout its life. C-14 is used to determine the age of fossils. In the upper atmosphere, neutrons present in cosmic rays are captured to cause the following nuclear reaction.

7N14 + 0n1 6C14 + 1H1

The C-14 isotope circulates in the atmosphere and is absorbed by living organisms during photosynthesis. The ratio of C-14 to C-12 in living organisms is 1:1012. Once the living organism dies, the C-14 level in the dead organism decreases due to the following reaction.

6C14 7N14 + -1e0 + γ-rays

The death of the plant ends its ability to absorb C-14. Half of the

The lifespan of C-14 is 5770 years. If the concentration of C-14 in

By comparing the living plant and the piece of dead material at a certain point in time, the age of the material (fossil) can be determined.

(I)

Describe the relationship between the decay constant and the half-life.

(Retrieve)

(iii)

In a piece of dead wood, the activity or concentration of C-14 is one-third of its original activity. Calculate the age of the old wood.

(Application)

(iii)

The half-life (t1/2) of a first-order reaction is 30 minutes. Calculate the time required for 87.5% of the reaction to complete.

(Application)