Explanation

(d)
In $C_{6}H_{5}$ ring there are three $\pi$-bonds and one $\pi$-bond is present in [image:12_image354.emf] group.
Therefore, in all there are four $\pi$- bonds in $C_{6}H_{5}COOH.\$In $CH_{3}CH_{2}COCH_{3}$there is only one $\pi$-bond in $C = O\$group, in $CH_{2} = CH - CH = CH_{2}\$there are two $\pi$-bonds while in $HC \equiv C - CH = CH_{2}$ there are three $\pi$- bonds