Which functional group is in ethanol (C₂H₅OH)?

**The reasoning** Ethanol's formula is C₂H₅OH. Breaking it down: C₂H₅ is the ethyl group (the carbon chain), and —OH is the functional group attached to it. The —OH group is called a **hydroxyl group**, and it defines **alcohols**. Any organic compound with —OH attached to a carbon chain is an alcohol. So ethanol = ethyl + alcohol = C₂H₅OH. Think of functional groups as the "identity cards" of organic compounds — they determine the compound's name and properties. **Why the wrong options tempt you** - **A) —COOH** (carboxyl group) defines carboxylic acids like ethanoic acid (CH₃COOH). Students mix this up because both have "OH" in them, but —COOH has a C=O attached. - **C) —CHO** (aldehyde group) is found in compounds like ethanal (CH₃CHO). The confusion comes from similar names (ethanol vs ethanal). - **D) —NH₂** (amino group) defines amines. Some guess this randomly without analyzing the formula. **Quick takeaway** Always look for the functional group *directly in the formula* — if you see —OH alone, it's an alcohol; the compound name will end in "-ol."