Question

Fifth group elements form hydrides of type `AH_3`.The hydrides have a lone pair of electrons.The hydrides 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 point depends on their ability to form hydrogen bond and their molecular size which which decide the intermolecular forces in the hydrides.
The boiling poins of the hydrides of V-group elements are in the order :
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 1

Correct Answer - C
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`.