Question

Which hydride amongst the following has the least boiling point?

• A. $N{H}_3$
• B. $P{H}_3$
• C. $As{H}_3$
• D. $B{F}_3,P{F}_5$
• E. $Bi{H}_3$

Answer 1

Answer: (B)

(a) $N{H}_3\to$ Inspite of small size of $N$ -atoms. It has strong H-bonds due to high electronegativity of nitrogen. Thus has high boiling point.

(b) $P{H}_3\to$ Due to the small size of $P$ -atoms, it has least van der Walls force and will not form intermolecular H-bonds.

(c) $As{H}_3\to$ It has larger As-atoms which provides more van der Walls force.

(d) $B{F}_3\cdot P{F}_5\to$ It has also larger molecular size than that of $P{H}_3$ and $As{H}_3$, thus has more van der Walls force.

(e) $Bi{H}_3\to$ It has larger size than that of $P{H}_3$, thus offers more van der Walls force. Thus $P{H}_3$ has least boiling point.