Question

what is the structure of 1 - ethyl - 2 - methylcyclohexane?

Explanation:

1 - ethyl - 2 - methylcyclohexane has a cyclohexane ring. The ethyl group ($-C_2H_5$) is attached to the first carbon of the ring and the methyl group ($-CH_3$) is attached to the second carbon of the ring. Analyzing the given structures, the correct structure should have a cyclohexane ring with an ethyl and a methyl group at appropriate positions.

Answer:

The second option (the one with a cyclohexane ring having an ethyl group on one carbon and a methyl group on an adjacent carbon) is correct.