Final answer:
Thiols are the class of compound most likely to have an offensive odor due to their sulfur content and propensity to be detected by the human nose at low concentrations.
Step-by-step explanation:
The compound class most likely to have an offensive odor is thiols. Thiols, also known as mercaptans, are sulfur analogs of alcohols and are characterized by their general formula RSH. One characteristic feature of thiols is their strong, often unpleasant odor, which is detectable by the human nose at very low concentrations. For instance, thiols are added to odorless natural gas to help detect leaks, and compounds like methanthiol contribute to the odor of foods such as oysters and onions. In contrast, other classes of compounds like alkanes, ethers, and alkenes typically do not have strong or offensive odors.