KEAM 2021 Physics and Chemistry Solved Paper

Iodoform test is given by those compounds which has methyl ketone moiety. Hence, P is acetone.Fehling's solution gives red precipitate with aliphatic aldehydes. So, R is acetaldehyde.
Tollen's test is given by aldehydes, aromatic aldehydes and α-hydroxy ketones. So, Q is benzaldehyde.The remaining compound S did not give any test. So, it is diethyl ketone.
Therefore, P= Acetone, Q= Benzaldehyde, R= Acetaldehyde and S= Diethyl ketone