Compound A, $C_5{H}_{10}O$  forms a phenyl hydrazone and gives negative Tollen's and iodoform test compound A, on reduction gives n-pentane. A is :

Compound (A) $C_5{H}_{10}O$ is a carbonyl compound because it generates a phenyl hydrazone.
Compound A fails the Tollen's test, indicating that it is a ketone and not an aldehyde. As opposed to kutone, aldehydes produce a positive Tollen's test result.