Answer the question on basis of passage given below:
Nitrogen differs from the rest of the members of its group due to its small size, high electronegativity, high ionisation enthalpy and non-availability of d-orbitals. Nitrogen has unique ability to form \(p\pi-p\pi\) multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O). Heavier elements of this group do not form \(p\pi-p\pi\) bonds as their atomic orbitals are so large and diffused that they cannot have effective overlapping.
Most stable hydride amongst the following is:
(A) \(NH_3\)
(B) \(PH_3\)
(C) \(AsH_3\)
(D) \(SbH_3\)
(E) \(BiH_3\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) Only
The stability of the group 15 hydrides depends on the strength of the E–H bond. Down the group the central atom becomes larger, its orbitals overlap less with the 1s orbital of hydrogen, and the E–H bond dissociation enthalpy decreases. So the stability falls in the order:
\( \ce{NH3} \) > \( \ce{PH3} \) > \( \ce{AsH3} \) > \( \ce{SbH3} \) > \( \ce{BiH3} \)
(A) NH3 — Correct. The small N atom forms the strongest E–H bond, so \( \ce{NH3} \) is the most stable hydride.
(B) PH3 — Incorrect. The P–H bond is weaker than N–H, so \( \ce{PH3} \) is less stable than \( \ce{NH3} \).
(C) AsH3 — Incorrect. Still weaker As–H bond; less stable.
(D) SbH3 — Incorrect. Weak Sb–H bond; it decomposes easily.
(E) BiH3 — Incorrect. \( \ce{BiH3} \) has the weakest E–H bond and is the least stable of all.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Reactivity towards Hydrogen – “… The hydrides show regular gradation in their properties. The stability of hydrides decreases from NH3 to BiH3 which can be observed from their bond dissociation enthalpy. Consequently, the reducing character of the hydrides increases.”