Give reasons for the following :
(A) `(CH_(3))_(3)P=O` exists but `(CH_(3))_(3)N=O` does not.
(B) Oxygen has less electron gain enthalpy with negative sigh than sulphur.
(C ) `H_(3)PO_(2)` is stronger reducing agent than `H_(3)PO_(3)`.

Explanation

(A) As N can.t form 5 covalent bonds/its maximum covalency is four.
(B) This is due to very small size of oxygen atom/repulsion between electrons is large in relatively small 2p sub-shell.
(C ) In `H_(3)PO_(2)` there are 2 P-H bonds, whereas in `H_(3)PO_(3)` there is 1 P-H bonds.