Among the following functional groups, which is the least reactive?

• A. $\text{Alkane}$
• B. $\text{Carboxylic acid}$
• C. $\text{Aldehyde}$
• D. $\text{Alcohol}$

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of reactivity in organic functional groups. Reactivity generally depends on the presence of polar bonds, the stability of intermediates, and the ability to undergo chemical transformations.
2. Step 2: Analyze each functional group: Alkanes have only C–C and C–H single bonds, which are relatively nonpolar and strong, making them less reactive under normal conditions.
3. Step 3: Carboxylic acids contain a highly polar carbonyl group (C=O) and an acidic hydroxyl group (–OH), making them reactive in acid-base and nucleophilic substitution reactions.
4. Step 4: Aldehydes have a polar carbonyl group (C=O) that is highly electrophilic, making them reactive towards nucleophiles and oxidation reactions.
5. Step 5: Alcohols contain a polar O–H bond, which can participate in hydrogen bonding and various substitution and oxidation reactions, making them more reactive than alkanes.