Isomerism is a phenomenon where by two or more compounds have the same molecular formula but different structural patterns. The compounds involved are called isomers.
Now, let us consider the molecular formula of the two compounds given in the question above.
The two compounds given in the question above have different molecular formula
Benzene has molecular formula as C6H6
Cyclohexane has molecular formula as C6H12.
Since their molecular formula are different, therefore, they are not isomers..
