Question

Which one has the lowest boiling point?

• A. $N{H}_3$
• B. $P{H}_3$
• C. $AsC{I}_3$
• D. $Sb{H}_3$

Answer 1

Answer: (B)

In the hydrides of group number five, the boiling points changes as ${}_{238.5K}^{N{H}_3>}{}_{185.5K}^{P{H}_3}{}_{254.6K}^{<As{H}_3}{}_{254.6K}^{<Sb{H}_3}{}_{290K}^{<Bi{H}_3}$ $\therefore$ Generally mass increases then boiling point increases. The higher boiling point of $N{H}_3$ is due to excessive hydrogen bonding, so $P{H}_3$ have lowest boiling point among hydrides of group number 15, i.e. nitrogen family.