Question

$P{H}_3$ has lower boiling point than $N{H}_3$. Why?

Answer 1

Boiling point of $N{H}_3\text{and}P{H}_3$

In ammonia $\left(N{H}_3\right)$, the molecules are linked by intermolecular hydrogen bonding. Due to this we need high amount of energy to break these hydrogen bond for boiling.

But $P{H}_3$ molecules are not associated through hydrogen bonding, so it boils easily as compared to $N{H}_3$.

That is why the boiling point of $P{H}_3$ is lower than $N{H}_3$.

Final answer: Due to intermolecular hydrogen bonding.