Solution:

One can differentiate between pentan-2-one and pentan-3-one by iodoform test. Pentan-2-one have a –CO-CH3 group and therefore forms a yellow precipitate of Iodoform. Pentan-2-one gives a positive iodoform test, whereas, and pentan-3-one does not give a positive iodoform test because they don’t have a –CO-CH3 group.