Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?
Atomic size increases down the group and thus the stability of the hydrides of Group-15 elements decreases. Now, the least stable hydride is the one which is more reactive and possessing higher reducing strength. The reducing character of hydrides increases on moving from NH3 to BiH3. Hence, BiH3 is the strongest reducing agent among hydrides of Group-15 elements.