Which of the following reagents can be used to oxidise primary alcohols to aldehydes? (i) CrO3 in an anhydrous medium. (ii) KMnO4 in acidic medium. (iii) Pyridinium chlorochromate. (iv) Heat in the presence of Cu at 573K

Option (i), (iii) and (iv) are the answers.

Primary alcohols can be oxidised to aldehydes using CrO3 in an anhydrous media. CrO3 serves as an oxidizer in this situation. As a result, option I is the right answer.

Primary alcohols can also be oxidised to their corresponding aldehydes using pyridinium chlorochromate (PCC). As a result, option (iii) is the right answer.
Dehydrogenation or heating in the presence of Cu at 573K can also convert primary alcohols to their corresponding aldehydes. As a result, option (iv) is the right answer.