JEE Chemistry 2025 Question with Solution

Given: Two statements about group $15$ elements are to be checked.

Find: Which option correctly identifies the truth value of Statement I and Statement II.

Statement I: The $N-N$ single bond is weaker and longer than the $P-P$ single bond.

For bond length, atomic size increases down the group, so the $P-P$ bond is longer than the $N-N$ bond. The solution states approximate bond lengths as:

$$N-N \approx 147 \, \text{pm}, \qquad P-P \approx 222 \, \text{pm}$$

Hence, the claim that $N-N$ is longer is false.

For bond strength, the $N-N$ single bond is weaker because the small nitrogen atoms have significant lone pair-lone pair repulsion. The solution gives approximate bond energies as:

$$E_{N-N} \approx 160 \, \text{kJ mol}^{-1}, \qquad E_{P-P} \approx 200 \, \text{kJ mol}^{-1}$$

So the part saying $N-N$ is weaker is true, but the part saying it is longer is false. Therefore, Statement I is false.

Statement II: Compounds of group $15$ elements in $+3$ oxidation states readily undergo disproportionation reactions.

This is not true for all group $15$ elements. The solution notes that nitrogen and phosphorus can show disproportionation in the $+3$ oxidation state, for example:

$$3\text{HNO}_2 \rightarrow \text{HNO}_3 + 2\text{NO} + \text{H}_2\text{O}$$ $$4\text{H}_3\text{PO}_3 \rightarrow 3\text{H}_3\text{PO}_4 + \text{PH}_3$$

But for heavier elements such as As, Sb, and especially Bi, the $+3$ oxidation state becomes more stable due to the inert pair effect, so they do not readily undergo disproportionation. Therefore, the statement is an incorrect generalization.

So, Statement II is false.

Conclusion: Both Statement I and Statement II are false. The correct option is B.

Given: Compare the trends in bond length, bond strength, and stability of the $+3$ oxidation state in group $15$.

Find: The correct option without lengthy analysis.

Use two direct trends:

1. Down a group, atomic size increases, so bond length increases. Therefore,

$$P-P \text{ bond is longer than } N-N$$

So Statement I is immediately false because it says $N-N$ is longer.

2. The $+3$ oxidation state is not uniformly prone to disproportionation across all group $15$ elements. Due to the inert pair effect, the $+3$ state becomes more stable for heavier elements like As, Sb, and Bi. So Statement II is also false.

Therefore, both statements are false, so the correct option is B.