Which of the following reagents can not be used to oxidise primary alcohols to aldehydes?

KMnO4 in acidic medium H2SO4 Copper dust at high temperature CrO3 in anhydrous medium

KMnO4 in acidic medium

KMnO4 in acidic medium cannot be used to oxidize primary alcohols to aldehydes. The oxidation will not stop at aldehyde stage.