Among the hydrides of Group-15 elements, which have the
(a). lowest boiling point?
(b). maximum basic character?
(c). highest bond angle?
(d). maximum reducing character?

The stability of hydrides decreases from NH₃ to BiH₃ which can be observed from their bond dissociation enthalpy. Consequently, the reducing character of the hydrides increases. Ammonia is only a mild reducing agent while BiH₃ is the strongest reducing agent amongst all the hydrides. Basicity also decreases in the order NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃. Due to high electronegativity and small size of nitrogen, NH₃ exhibits
hydrogen bonding in solid as well as liquid state. Because of this, it has higher melting and boiling points than that of PH₃. Highest bond angle is in ammonia as nitrogen has highest electron density, repulsion between lone pairs and bond pairs will be more resulting into more bond angle due to small size of nitrogen.

So, the right answers are a. PH₃ b. NH₃ c. NH₃ d. BiH₃