Question

BiH3 is the strongest reducing agent amongst allthe hydrides of group 15 elements why?

Answer 1

As bond length of M-H increases down the group, the bond strength of M-H bond decreases down the group(where M is the element of 15th group). Which implies that the bond dissociation energy of Bi-H is quite less and hence can be dissociate easily. Therefore BiH3 readily undergoes oxidation and acts as a strong reducing agent.