Increasing order of reducing power of following hydrides would be
- \(SbH_3\)
- \(AsH_3\)
- \(NH_3\)
- \(PH_3\)
- \(BiH_3\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C < D < B < A < E
Down group 15 the central atom becomes larger, the E–H bond becomes longer and weaker, and the bond dissociation enthalpy falls. A hydride with a weaker E–H bond gives up hydrogen more readily, so the reducing character increases down the group:
\( \ce{NH3} \) < \( \ce{PH3} \) < \( \ce{AsH3} \) < \( \ce{SbH3} \) < \( \ce{BiH3} \)
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 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. Ammonia is only a mild reducing agent while BiH3 is the strongest reducing agent amongst all the hydrides.”