Question

Which of the following has the lowest melting point?

Answer 1

Down the group, the melting point of hydrides generally increases due to increase in van der Waals forces. But due to the presence of $H$-bonding in $N{H}_3$ its melting point is the highest among group $15$ hydrides. Therefore, $P{H}_3$ has the lowest boiling point in group $15$ hydrides.