Chemistry - Complete P-block Question with Solution | TestHub

The reducing character of the hydrides of Group $15$ elements increases from ${\mathrm{NH}}_3$ to ${\mathrm{BiH}}_3$ (Bismuthine) because the reducing character depends upon the stability of the hydride.The greater the unstability of hydride,the greater is the its reducing character. Since,the ${\mathrm{BiH}}_3$ is the least stable (because the size of central atom is greatest & therefore its tendency to form stable covalent bond with small hydrogen atom decreases,as a result the bond strength decreases) in this series,hence the reducing character increases.