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 .
The boiling points of the hydrides of V-group elements are in the
order :

Options

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

Answer

C

Explanation

Due to increase in size from `PH_3` to `SbH_3` the van der Waals forces increase.So their boiling points increase from `PH_3` to `SbH_3`.But does to intermolecular hydrogen bonding, `NH_3` has very high boiling point but less than that of `SbH_3`.