Question

Arrange group 15 hydrides in the decreasing order of their reducing power​

Answer 1

the group 15 hydrides have been arranged in the decreasing order of their reducing power as follows:

To arrange the group 15 hydrides in its reducing power so to arrange them we have to arrange it on  the basis of lowering of dissociation Enthalpy and increasing in bond length from NH3 to HBi3

.

NH3<PH3<HAs3<HSb3<HBi3

From Nitrogen to Bismuth in group 15 there is an increase in their bond length of hydrides and decrease in dissociation enthalpy.