An organic compound (A), $C_9H_{10}O$, gives a 2,4-DNP reaction, negative Tollens' test and iodoform test. On drastic oxidation with chromic acid, it forms B, having molecular formulae, $C_7H_6O_2$. Identify A and B.

A: Propiophenone, B: Benzoic acid

The correct answer is Option (2) → A: Propiophenone, B: Benzoic acid

Compound A is propiophenone and compound B is benzoic acid.

• A gives 2,4-DNP test, so it must contain a carbonyl group (aldehyde or ketone).
• It gives negative Tollens’ test, so it is not an aldehyde $\rightarrow$ it is a ketone.
• It gives iodoform test, which is given by compounds having $-\text{CO}-\text{CH}_3$ (methyl ketone) group.

$\rightarrow$ So A must be a methyl ketone attached to a phenyl ring, i.e. propiophenone ($\text{C}_6\text{H}_5-\text{CO}-\text{CH}_2\text{CH}_3$).

• On strong oxidation (chromic acid), side chains attached to benzene ring get oxidized to $-\text{COOH}$, forming benzoic acid ($\text{C}_7\text{H}_6\text{O}_2$).

Thus,

A = Propiophenone

B = Benzoic acid