Question

How to distingusish between ethanal and propnal?

Answer 1

Aldehydes having at least one methyl group linked to the carbonyl carbon atom respond to iodoform test. They are oxidized by sodium hypoiodite (NaOI) to give iodoforms. Ethanal having  a methyl group responds to this test, but propanal does not.

Answer 2

aldehydes will have at least methyl group linked