Question

Boiling points of NH3 and HF areabnormally high as compared to those of hydrides of other elements in their respective groups.

Answer 1

The first element of the groups has smaller radii , owing to this they are also highly electronegative and form hydrogen bond. which increases the boiling points of NH3 and HF exceptionally higher than the other elements

Answer 2

NH3- Ammonia NH3 forms intermolecular hydrogen bonds wih each other,hydrogen bond is very strong,hence bond enthalpy increases leading to the increase in boiling point , moreover nitrogen being the smallest in the group have higher attraction force by the nucleus hence they have higher boilin point compared to all other hidrides of group 15 elements

HF- in HF ,the Flourine atoms is the atom with highest electronegetvity,hence pulling the shared pair of electron to itself.Hence having higher bond enthalpy and higher boiling point compared to all other hidrides of group 17 elements