The reaction, $$3Cl{O^ - }\left( {aq} \right) \to ClO_3^ - \left( {aq} \right) + 2C{l^ - }\left( {aq} \right),$$        is an example of

Solution :
TIPS/Formulae :
(i) In a disproportionation reaction same element undergoes oxidation as well as reduction during the reaction.
(ii) In decomposition reaction a molecule breaks down to more than one atoms or molecules
$$\mathop {3ClO_{\left( {aq} \right)}^ - }\limits^{ + 1} \mathop { \to ClO_3^ - }\limits^{ + 5} + \mathop {2Cl_{\left( {aq} \right)}^ - }\limits^{ - 1} $$
It is disproportionation reaction because $$Cl$$ is both oxidised $$\left( {{\text{ + 1}}\,{\text{to}}\,{\text{ + 5}}} \right)$$   and reduced $$\left( {{\text{ + 1}}\,{\text{to}}\, - 1} \right)$$   during reaction.