The trend of reducing abilities of the hydrides of group 15 are NH3<PH3<AsH3<SbH3<BiH3 The reducing character of the hydrides of group V elements depends upon the stability of hydrides. With progressive decrease in stability, the reducing character of hydrides increases as we move down the group. Thus, ammonia being stable has least reducing ability. The order of reducing abilities of V group hydrides is NH3<PH3<AsH3<SbH3<BiH3