Identify the correct IUPAC name of the given compound:

The correct answer is Option (1) → 4-Methylpent-3-en-2-one

For the IUPAC name of a carbonyl compound with a double bond, choose the longest chain that contains the C=O group and the C=C bond, and number it so that the carbonyl carbon gets the lowest number. The ketone is shown by the suffix –one and the double bond by –en–.

The compound is \( \ce{(CH3)2C=CH-CO-CH3} \). The longest such chain has five carbons. Numbering from the end nearer the C=O group, C-1 is the \( \ce{CH3} \) next to the carbonyl group, C-2 is the carbonyl carbon, C-3 and C-4 carry the double bond (with the methyl branch on C-4), and C-5 is the other terminal \( \ce{CH3} \).

The carbonyl group is at C-2, the double bond starts at C-3, and a methyl group is on C-4. So the name is 4-methylpent-3-en-2-one; its common name is mesityl oxide.

NCERT (2026-27 edition):
IUPAC Names – …