Question

To become a carbohydrate a compound must contain at least:

• A. 2 carbons
• B. 3 carbons
• C. 4 carbons
• D. 6 carbons

Hint:

Smallest carbohydrate = triose (3 carbons) → e.g., glyceraldehyde.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones. The simplest molecules that fit this definition and are optically active are the trioses.
Step 2: Detailed Explanation:
1. A carbohydrate must have at least one carbonyl group (aldehyde or ketone) and multiple hydroxyl (\( -\text{OH} \)) groups.
2. To have at least one chiral center (making it optically active), an aldose must have at least 3 carbon atoms.
3. The simplest carbohydrates (trioses) are Glyceraldehyde (an aldotriose) and Dihydroxyacetone (a ketotriose).
4. Both of these molecules have exactly 3 carbon atoms. Compounds with only 2 carbons (like glycolaldehyde) are often considered the precursor but the formal classification of "sugars" starts from trioses.
Step 3: Final Answer:
A compound must contain at least 3 carbon atoms to be classified as a carbohydrate.