Fifth group elements form hydrides to type `AH_(3)`. The hydrides have a lone pair of electrons. The hydries are reducing in nature and the reducing power is related to the stability of A-H bonds. The hydrides are covalent and low boiling. Their boiling points depends on their ability to from hydrogen bond and their molecular size which decide the intermolcular forces in the hydrides .
Reducing power of V-group hydrides are in order :

Options

A. `NH_3 gt PH_3 gt AsH_3 gt SbH_3 gt BiH_3`
B. `BiH_3 gt SbH_3 gt AsH_3 gt PH_3 gt NH_3 `
C. ` PH_3 gt NH_3 gt AsH_3 gt SbH_3 gt BiH_3`
D. `BiH_3 gt SbH_3 gt AsH_3 gt NH_3 gt PH_3 `

Answer

B

Explanation

A-H bond energy decreases with increase in size of A.Hence Bi-H bond readily breaks to make it the best reducer and the reducing power decrease of size of A.