The molecule CH3CH=CHCH3 is an alkene with the molecular formula C4H8. The isomerism exhibited by this molecule is geometrical isomerism cis-trans isomerism due to the presence of a carbon-carbon double bond.There are two isomers of this molecule:1. Z -but-2-ene cis-but-2-ene : In this isomer, the two methyl CH3 groups are on the same side of the double bond.2. E -but-2-ene trans-but-2-ene : In this isomer, the two methyl CH3 groups are on opposite sides of the double bond.So, the molecule CH3CH=CHCH3 has two isomers.