Why `KMnO_(4)` is stored in dark bottle and water happens to it's aidic solution?

Explanation

`MnO_(4)^(-)` solutions are intrinsically unstable in acidic solution and decompose slowly. This decomposition is catalysed by sun light. This is the statement-2 for which `KMnO_(4)` solution is kept in dark bottles.
`4MnO_(4)^(-)+4H^(+)overset(hv)to4MnO_(2)+3O_(2)+2H_(2)O`