Hypochlorite is a strong oxidant and bleaching agent. Why? 

Explanation

Hypochlorite, `OCl^(-)` is formed in the ground state of oxygen.
`OCl^(-)` bond is a single bond. `OCl^(-)` has no tendency to form pi bond and also it is not stabilised by resonance. It is less stable and provides nascent oxygen by decomposition.
`OCl^(-)rarr Cl^(-)+(O)`
Hence, `OCl^(-)` hypochlorite is good oxidant and powerful bleaching agent.