Statement - I : OX^– on heating in the presence of OH^– gives X– and ${\mathrm{XO}}_3^{-}$ (X = Cl, Br, I,)
Statement - II : Conversion of OX^– to X^– and ${\mathrm{XO}}_3^{-}$ is called disproportionation

OX^– $\stackrel{∆}{\to }$ X^– +${\mathrm{XO}}_3^{-}$ where  (X = Cl, Br, I,)

Disproportionation reaction is a type of redox reaction in which the same element undergoes oxidation and reduction simultaneously. 

oxidation number of  X  in  OX^– changes  from +1 to -1 and + 5   indicating that it undergoes  both oxidation and reduction .