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

Explanation

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