Which of these is a thiol?

• A. —SH
• B. —COH
• C. —OH
• D. None of the listed responses is correct.

Answer: (D)

Verified step by step guidance

1. Identify the functional group associated with a thiol. A thiol contains a sulfhydryl group, which is represented by the chemical structure $—SH$.
2. Examine each of the given options to determine if any match the structure of a thiol.
3. The first option, $—SH$, matches the structure of a thiol, as it contains the sulfhydryl group.
4. The second option, $—COH$, represents an aldehyde group, not a thiol.
5. The third option, $—OH$, represents a hydroxyl group, which is characteristic of alcohols, not thiols.