Which is the correct sequence in the following properties? For the correct order mark (T) and for the incorrect order mark (F) :
(i) Melting point : `NH_(3) gt SbH_(3) gt AsH_(3) gt PH_(3)`
(ii) Boiling point : `NH_(3) gt SbH_(3) gt AsH_(3) gt PH_(3)`
(iii) Dipole moment order : `NH_(3) gt SbH_(3) gt AsH_(3) PH_(3)`

Options

A. TFT
B. FTF
C. FFT
D. FFT

Answer

A

Explanation

(i) (T), M.P of `NH_(3)` is highest due to intermolecular H-bonding in it. Next lower M.P. will be of `SbH_(3)` followed by `AsH_(3)` due to high mol. Wt. of `SbH_(3)`.
(ii) (F), B.P. increase from `PH_(3) " to "SbH_(3) " via "AsH_(3)` due to increase in mol.wt. ` NH_(3)` does not follow this trend due to inter molecular H-bonding.
Increasing B.P. order : `PH_(3) lt AsH_(3) lt NH_(3) lt SbH_(3)`
(T) : Value of bond moment decreases.