Answer:
cis-1-Ethyl-2-propylcyclopropane <1-Cyclopropylpentane <cis-1,4-Dimethylcyclohexane <Ethylcyclohexane
Step-by-step explanation:
The least is the number of additives especially at the position 1,4 of the cyclohexane, the more is the stability.
Hence, the correct order of increasing stability is
cis-1-Ethyl-2-propylcyclopropane <1-Cyclopropylpentane <cis-1,4-Dimethylcyclohexane <Ethylcyclohexane