question_answer 2)

Why is BiH3 the strongest reducing agent amongst all the hydrides of Groups 15 elements?

Answer:

As we move down the group, the size of the element increases and, therefore, the bond length of the M—H bond increases and its strength decreases. Thus as we move down the group, the M—H bond can break more easily to evolve H2 gas which acts as the reducing agent. Thus, BiH2 is least stable among the hydrides of group 15 and hence is the strongest reducing agent.