JAMB Chemistry 2023 Paper

Concept:A $\pi$ bond is found only in a carbon–carbon double bond. For a normal alkene, one double bond contributes exactly one $\pi$ bond.Explanation:A simple open-chain alkene with six carbon atoms has the molecular formula $C_6H_{12}$.Compared with the saturated alkane $C_6H_{14}$, it has lost only two hydrogen atoms. This shows that the molecule has only one carbon–carbon double bond.Each $C=C$ double bond is made up of one $\sigma$ bond and one $\pi$ bond. Therefore, the number of $\pi$ bonds in a standard six-carbon alkene is $1$.The phrase “six carbon atoms” alone is not enough to describe a polyene. A triene, tetraene, or pentaene would have a different number of $\pi$ bonds. So the options given do not match the usual meaning of a simple alkene.Answer:A normal six-carbon alkene contains 1 $\pi$ bond. Since 1 is not among the options, none of the given options is correct.