Which of the following compounds can exist as cis-trans isomers?

• A. ${\mathrm{CH}}_2\mathrm{CH}=\mathrm{CH}{\mathrm{CH}}_3$
• B. ${\mathrm{CH}}_3\mathrm{CH}=\mathrm{CH}H$
• C. ${\mathrm{CH}}_2\mathrm{CH}=\mathrm{CH}\mathrm{Cl}$
• D. ${\mathrm{CH}}_3\mathrm{CH}=\mathrm{CH}{\mathrm{CH}}_3$

Answer: (A)

Verified step by step guidance

1. Identify the structural requirement for cis-trans (geometric) isomerism: a double bond (C=C) where each carbon of the double bond has two different substituents.
2. Examine each compound to see if both carbons in the double bond have two different groups attached. If either carbon has two identical groups, cis-trans isomerism is not possible.
3. For the compound \( \mathrm{CH_2=CH-CH_2CH_3} \), check the substituents on each double-bonded carbon: the first carbon has two hydrogens (\( \mathrm{CH_2} \)), so no cis-trans isomerism is possible here.
4. For the compound \( \mathrm{CH_3-CH=CH-H} \), the second carbon has a hydrogen and a methyl group, but the first carbon has two hydrogens (one implied), so no cis-trans isomerism is possible.
5. For the compound \( \mathrm{CH_2=CH-Cl} \), check if both carbons have two different substituents. If yes, then cis-trans isomerism can exist; if not, it cannot.