i. The organic compound (A) is 2-Ethylbenzaldehyde

ii. Its molecular formula is C9H10O.
iii. Since it is an aldehyde, it can form 2,4-DNP derivative and can reduce Tollens’ reagent. It can also undergo Cannizzaro reaction, as it does not contain α - H atom.
iv. On vigorous oxidation, both-CHO group and the ethyl side chain are oxidized to -COOH groups to give 1,2-benzene dicarboxylic acid HOOC - C6H4 - COOH.