KEAM 2021 Physics and Chemistry Solved Paper

A research scholar returned to the laboratory after the lock down due to Covid-19. He kept acetone, benzaldehyde, acetaldehyde and diethyl ketone in four different bottles. The bottles contained only the label as P,Q,R and S. He forgot which bottle contained which compound. Compounds P and R only underwent iodoform test. Compound R alone gave reddish brown precipitate with Fehling's reagent. Compounds Q and R alone underwent Tollen's test. Compound S did not answer any of the above tests.
Identify the compounds P,Q,R and S.