Which of the following functional groups is most likely responsible for an organic molecule behaving as a base?

• A. Hydroxyl group ($\mathrm{OH}$)
• B. Aldehyde group ($\mathrm{CHO}$)
• C. Amino group ($\mathrm{NH}{2}_{}$)
• D. Carboxyl group ($\mathrm{COOH}$)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of basicity in organic molecules. A base is a species that can accept a proton (H\textsuperscript{+}). Therefore, the functional group responsible for basic behavior must have a lone pair of electrons available to accept a proton.
2. Step 2: Analyze each functional group for the presence of lone pairs and their ability to accept protons. The hydroxyl group (OH) has lone pairs on oxygen but is generally neutral or weakly acidic, not strongly basic.
3. Step 3: Consider the aldehyde group (CHO). The carbonyl carbon is electrophilic, and the oxygen has lone pairs, but aldehydes typically do not act as bases; they are more reactive as electrophiles.
4. Step 4: Examine the amino group (NH\textsubscript{2}). Nitrogen has a lone pair of electrons that is readily available to accept a proton, making amino groups basic in nature.
5. Step 5: Look at the carboxyl group (COOH). It contains acidic hydrogen and tends to donate protons rather than accept them, so it behaves as an acid rather than a base.