Elements of group- 15, 16, and 17 form compounds with hydrogen with general formula \(MH_3\), \(H_2M\), and \(HX\) (called hydrogen halides). The stability of these hydrides, along with \(M-H\) bond strength and basic nature decreases down the group. Boiling point of these hydrides mainly depends on the strength of their intermolecular forces.
The decreasing order of boiling point of group 15 hydrides 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 4
The correct answer is Option (4) → BiH3 > SbH3 > NH3 > AsH3 > PH3
Down Group 15 the hydrides get bigger and heavier, so the van der Waals forces and boiling points rise from \( \ce{PH3} \) to \( \ce{BiH3} \). \( \ce{NH3} \) is the exception: its molecules are linked by hydrogen bonds, which lift its boiling point above those of \( \ce{PH3} \) and \( \ce{AsH3} \).
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
