Account for the following : (a) Chlorine water has both oxidising and bleaching properties.
(b) `H_(3)PO_(2) and H_(3)PO_(3)` act as good reducing agents while `H_(3)PO_(4)` does not.

Explanation

(a) In presence of moisture or water, `Cl_(2)` gives nascent oxygen which is responsible for its oxidising and bleaching properties as shown below :
`Cl_(2) + H_(2)O rarr ,HCl + HClO' rarr 2HCl + underset("Nascent oxygen")([O])`
(i) It oxidises acidified ferrous sulphate to ferric sulphate
`{:(" "Cl_(2)+H_(2)O rarr 2HCl + O),(" "FeSO_(4)+H_(2)SO_(4) + O rarr Fe_(2)(SO_(4))_(3)+H_(2)O),(bar (underset(("Green"))(2FeSO_(4))+H_(2)SO_(4) + Cl_(2) rarr underset(("Brown"))(Fe_(2)(SO_(4))_(3))+2HCl)):}`
(ii) It bleaches vegetable and organic colouring matter to colourless substances by oxidation
`Cl_(2) + H_(2)O rarr 2HCl + [O]`
Vegetable colouring matter `+ O rarr` Oxidised colourless substances.
(b) The structures of `H_(3)PO_(2), H_(3)PO_(3) and H_(3)PO_(4)` are :
Due to the presence of P-H bonds, both `H_(3)PO_(2) and H_(3)PO_(3)` act as reducing agents. In contrast, `H_(3)PO_(4)` does not have any P-H bonds and hence it does not act as a reducing agent.

(c) `O_(3)` is a powerful oxidising agent. Therefore, it oxidises aq. KI to violet vapours of `I_(2)`
`{:(" "O_(3)(g) rarr O_(2)(g) + O(g)),(" "2KI (aq) + H_(2)O (l) + O(g) rarr 2KOH (aq) + I_(2)(s)),(bar(underset(("Colourless"))underset("Potassium iodide")(2KI(aq))+H_(2)O (l) + O_(3)(g) rarr 2KOH (aq) + O_(2)(g)+underset(("Violet"))underset("Iodine")(I_(2)(s)))):}`