Assign reason for the following :
(i) `H_(3)PO_(2)` is a stronger reducing agent than `H_(3)PO_(4)`.
(ii) Sulphur shows more tendency for catenation than oxygen.
(iii) Reducing character increases from HF to HI.

Explanation

In `H_(3) overset(+1)(PO_(2))`, the oxidation state of P can increase upon `+5`. But in `H_(3) overset(+5)(PO_(4))`. P atom is already in highest oxidation state `(+5)`. Therfore, `H_(3)PO_(2)` acts as stronger reducing agent than `H_(3)PO_(4)`. In fact, the latter can act only as oxidising agent.
(ii) N/A
(iii) N/A