In the IUPAC system, aliphatic carboxylic acids are named by replacing the ending –e in the name of the corresponding alkane with –oic acid. In numbering the carbon chain, the carboxylic carbon is numbered one. For naming compounds containing more than one carboxyl group, the alkyl chain leaving carboxyl groups is numbered and the number of carboxyl groups is indicated by adding the multiplicative prefix, dicarboxylic acid, tricarboxylic acid, etc. to the name of parent alkyl chain. The position of –COOH groups are indicated by the arabic numeral before the multiplicative prefix.

What is the IUPAC name of the given compound? 

 3-Phenylpropanoic acid

The correct answer is option 4.  3-Phenylpropanoic acid.

The compound has the group (-CH₂CH₂COOH) directly attached to a benzene ring. The preference is given to the carboxyl group and the compound is named as a carboxylic acid derivative. There are total three carbons making it propanoic acid with the benzene ring as substituent on the last carbon (C-3) as a phenyl group.