JEE Main 2025 Apr 3 Shift 1, Chemistry Q17: Mechanism of Some Important Reactions of Alkenes

Reductive ozonolysis (${\text{O}}_3$ followed by $\text{Zn}/{\text{H}}_2\text{O}$) cleaves a C=C bond, replacing each sp${}^2$ carbon with a carbonyl group while preserving all other substituents.

The target 3-methyl-6-oxoheptanal has the skeleton ${\text{OHC-CH}}_2{\text{-CH(CH}}_3{\text{)-CH}}_2{\text{-CH}}_2{\text{-CO-CH}}_3$: an aldehyde at one end and a methyl ketone at the other, with a methyl branch three carbons from the aldehyde.

Working backwards, stitch the two carbonyls into a single C=C. This gives a six-membered ring with a methyl group on one alkene carbon (becomes the methyl ketone) and a methyl branch elsewhere on the ring (gives the C3 methyl in the product). That is 1,4-dimethylcyclohex-1-ene, option (2).