Chemistry - Complete P-block Question with Solution | TestHub

The reducing character of hydrides of Group 15 elements (NH₃, PH₃, AsH₃, SbH₃, BiH₃) increases down the group. This is because the bond dissociation enthalpy of the E-H bond (where E is the Group 15 element) decreases as the size of the central atom increases. A lower bond dissociation enthalpy means the E-H bond is weaker and can be broken more easily, facilitating the donation of hydrogen and thus acting as a stronger reducing agent. ${\mathrm{BiH}}_3$ has the weakest Bi-H bond, making it the strongest reducing agent.