Functional group of alcohols.

**The reasoning** Alcohols are organic compounds that have one key feature: a hydroxyl group (—OH) attached to a carbon atom. Think of it like the "signature" that makes something an alcohol. For example, ethanol (the alcohol in drinks) is CH₃CH₂OH — notice that —OH at the end? That's what makes it an alcohol. The functional group —OH is what gives alcohols their characteristic properties: they can form hydrogen bonds, dissolve in water (to some extent), and react in specific ways. **Why the wrong options tempt you** - **—COOH** looks similar because it contains OH, but this is a carboxylic acid group (like in vinegar). The C=O makes it acidic, not alcoholic. - **—CHO** is an aldehyde group (like in formaldehyde). Students confuse it because aldehydes can be made *from* alcohols, but they're different families. - **—NH₂** is an amine group (contains nitrogen). Some students mix up all functional groups when cramming. **Quick takeaway** Remember: "Alcohol = OH attached to carbon" — just like how beer bottles have "OH" warnings! If you see —OH bonded to a carbon chain (not part of COOH), you've found an alcohol.