Question

Consider the statements related to group 15 hydrides.
(A) Stability of hydrides decreases down the group.
(B) Reducing nature of hydrides increases down the group.
(C) Lone pair donating tendency increases down the group.
(D) H–E–H bond angle decreases down the group.

• A. A, B and C are correct.
• B. A, B and D are correct.
• C. B and C are correct.
• D. A, C and D are correct.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
Analyze the periodic trends for the hydrides of nitrogen family ($NH_3$ to $BiH_3$).
Step 2: Detailed Explanation:
(A) Stability: As we move down the group, the size of the central atom (E) increases, causing the E-H bond length to increase and bond dissociation enthalpy to decrease. Thus, thermal stability decreases. (Correct)
(B) Reducing Nature: Since the E-H bond becomes weaker down the group, it becomes easier to release hydrogen. Thus, reducing character increases. (Correct)
(C) Lone pair donating tendency (Basicity): As the central atom's size increases, the electron density of the lone pair is distributed over a larger volume, making it less available for donation. Thus, basicity decreases down the group ($NH_3>PH_3>AsH_3 \dots$). (Incorrect)
(D) Bond Angle: As the central atom size increases and electronegativity decreases, the electron pairs of the bonds stay further from the nucleus, resulting in decreased bond-pair repulsion. Thus, the bond angle decreases ($NH_3 \approx 107.8^\circ$ to $BiH_3 \approx 90^\circ$). (Correct)

Statements A, B, and D are correct.
Step 3: Final Answer:
The correct statements are A, B, and D.