See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the compound: The structure shown is 1,2-disubstituted cyclopentane. Looking at the drawing, the cyclopentane ring has two substituents on adjacent carbons: one carbon bears an ethyl group (C2H5) and the other carbon bears a methyl or ethyl group, making it a disubstituted cyclopentane (specifically 1-ethyl-2-methylcyclopentane or similar 1,2-disubstituted cyclopentane). Step 2 - Concept of geometrical isomerism in cycloalkanes: Geometrical (cis-trans) isomerism in cycloalkanes occurs when there are two or more carbons in the ring each bearing two different substituents. For a 1,2-disubstituted cyclopentane where the two substituents on the ring carbons are different from each other, cis and trans isomers are possible. Step 3 - Count the geometrical isomers: For a 1,2-disubstituted cyclopentane with two different substituents (one being ethyl and one being methyl, or two different groups), there are exactly 2 geometrical isomers: the cis isomer (both substituents on the same face of the ring) and the trans isomer (substituents on opposite faces of the ring). Step 4 - Why other options fail: - Option (a) 0: Incorrect, because restricted rotation in the ring allows cis-trans isomerism to exist. - Option (c) 3: Incorrect, a simple 1,2-disubstituted cyclopentane with two different groups gives only 2 geometrical isomers, not 3. - Option (d) 4: Incorrect, 4 would require two stereocenters each with two different substituents in a more complex arrangement. Step 5 - Conclusion: The compound is a 1,2-disubstituted cyclopentane giving 2 geometrical isomers (cis and trans). Therefore, the correct answer is B.