Which line-angle formula represents an alkene?

Option 3.

Explanation:

Alkenes are generally unsaturated hydrocarbon with carbon to carbon double bond (C=C).

From the options given above, only option 2 and 3 contain carbon to carbon double bond (C=C).

Option 2 is called a benzene ring and not an alkene. Benzene are not classified as alkenes because the double bond between the carbon can not be broken i.e benzene does not undergo addition reaction like the alkenes. Benzene tends to show more stability than the alkenes.

This leaves us with option 3 as the answer to the question because it contains carbon to carbon double bond (C=C)