JEE Chemistry 2024 Question with Solution

Given: Statements A, B, C, D about hydrides of group 15 elements.

Find: Which statements are correct.

Concept used:

• Stability of group 15 hydrides decreases down the group because the $E-H$ bond dissociation enthalpy decreases.
• Reducing character increases down the group because the $E-H$ bond becomes weaker.
• Basicity decreases down the group because the lone pair becomes less available for donation.

Evaluate each statement:

1. Statement A says stability decreases in the order

$$NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$$

This is correct.

2. Statement B says reducing ability increases in the order

$$NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$$

This is correct.

3. Statement C says $NH_3$ is a strong reducing agent while $BiH_3$ is a mild reducing agent. This is incorrect. The actual trend is opposite: $NH_3$ is a very weak reducing agent, while $BiH_3$ is the strongest reducing agent among these hydrides.

4. Statement D says basicity increases down the group. This is incorrect. The correct basicity order is

$$NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$$

Therefore, the correct statements are A and B only. Hence, the correct option is C.