\({ \overset { 0 }{ C } l }_{ 2 }(g)+2{ \overset { -2 }{ O } }\overset { +1 }{ { H }^{ - } } (aq)\longrightarrow { \overset { +1 }{ C } l }\overset { -2 }{ { O }^{ - } } (aq)+{ \overset { -1 }{ C } l }^{ - }(aq)+{ \overset { +1 }{ H } }_{ 2 }\overset { -2 }{ O } (l)\)
In this reaction, oxidation number of Cl increases from 0 (in Cl₂) to 1(in ClO^-) as well as decreases from 0 (in Cl₂₎ to -1 (in Cl^-).So, it acts as both reducing as well as oxidising agent. This is an example of disproportionation reaction. In this reaction , ClO^- species bleaches the substances due to its oxidising action.[In hypochlorite ion (ClO^-), Cl can decrease its oxidation number from +1 to 0 or -1].
Note 
Disproportionation reactions are a special type of redox reactions in which an element in one oxidation state is simultaneously oxidised and reduced. 

In a disproportionation reaction, the same species simultaneously get oxidised as well as reduced.Therefore, for such a redox reaction to occur,the reacting species must contain an element which has atleast three oxidation states.The element, in reacting species,is present in an intermediate state while lower and higher oxidation states are available for reduction and oxidation states are available for reduction and oxidation to occur(respectively).Fluorine is the strongest oxidising agent.It does not show positive oxidation state. That's why fluorine does not show disproportionation reaction.

pH = -log[H⁺] = -log[3.8 x 10 ^-3 ] =2.4202 \(\approx \) 2.42

Explanation for the given statement the basis of ionisation and effect upon the concentration of sodium chloride is given below.
(i) Sugar being a nonelectrolyte does not ionise in water whereas NaCl ionise completely in water  and produces Na⁺ and Cl^- ion which help in the conduction  of electricity.
(ii) When concentration of NaCl is increased, more Na⁺ and Cl^- ions will be produced.Hence, conductance or conductivity of the solution increases.

Suppose that the oxidation number of P in \({ HPO }_{ 3 }^{ 2- }\)be x.
Theb, 1 + x + 3 (-2) = -2
or  x + 1 - 6 = -2 or x = +3