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 H-M-H bond angle of `V` group hydrides decrease from `107^(circ)` to `90^(circ)` for `NH_(3)` to `SbH_(3)` , this is due to:

Options

A. increase in strength of bases with molecualar weight
B. use of pure p-orbital M-H bonding in hydrides of higher moelcular weight
C. bond energies of M-H bonds increase
D. bond pairs of electrons go closer to central atom

Answer

B

Explanation

In successive hydrides starting from N to Sb, the lone pair cause distortion of M-H bonds. The bond angle decreases from `107^(circ)` "to" `90^(circ)`. This suggests that orbitals used in M-H bonding are almost pure p-orbitals.