Question

Carbohydrates are:
A. Organic compounds with a minimum three number of carbons
B. Polyhydroxy alcohols
C. Hydrates of carbon
D. Polyhydroxy aldehydes or ketone
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, C and D only
• C. B, C and D only
• D. A, B and C only

Hint:

Carbohydrates are defined as polyhydroxy aldehydes or ketones.
Sugar alcohols (like sorbitol and mannitol) are polyhydroxy alcohols, which are reduced derivatives of carbohydrates, not carbohydrates themselves.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Carbohydrates are the most abundant biomolecules on Earth, serving structural, energetic, and signaling roles in living systems.

Step 2: Detailed Explanation:
- Minimum three carbons (A): The simplest monosaccharides (trioses, like glyceraldehyde and dihydroxyacetone) possess exactly three carbons. No stable monosaccharide exists with fewer than three carbons. This statement is correct.
- Hydrates of carbon (C): Historically, carbohydrates were named because they conform to the general chemical formula \(C_n(H_2O)_m\), appearing as hydrates of carbon. This statement is correct.
- Polyhydroxy aldehydes or ketones (D): This is the precise modern chemical definition of carbohydrates. They are polyhydroxy aldehydes or polyhydroxy ketones (or substances that yield such compounds upon hydrolysis). This statement is correct.
- Polyhydroxy alcohols (B): Although sugars contain multiple hydroxyl groups, they are not simple alcohols; they must contain an aldehyde or ketone carbonyl group. Alcohols lacking these carbonyl groups are sugar alcohols (alditols), not true carbohydrates. This statement is incorrect.
Therefore, statements A, C, and D are correct.

Step 3: Final Answer:
The correct answer is A, C and D only, corresponding to option (B).