An acidified solution of KMnO₄ oxidizes

Acidified solution of KMnO₄ which is known as potassium permanganate helps in oxidizing sulphites to sulphates.

While nitrates,  ferric salts,  sulphates are not further oxidized.

Sulphates = ${\mathrm{SO}}_4^{2-}$ is +6

Sulphites = ${\mathrm{SO}}_3^{2-}$  is +4