Question

Sugars are

• A. Optically active polyhydroxy aldehydes
• B. Optically active polyhydroxy ketones
• C. Optically active polyhydroxy aldehydes or ketones
• D. Polyhydroxy aldehydes or ketones which may or may not be optically active

Hint:

Sugars are broadly polyhydroxy aldehydes or polyhydroxy ketones, or compounds that yield them on hydrolysis.

Answer 1

The Correct Option is D

Concept:
Sugars are carbohydrates. Carbohydrates are generally defined as polyhydroxy aldehydes or polyhydroxy ketones, or compounds that give such substances on hydrolysis.

Step 1: Understand polyhydroxy aldehydes.
Some sugars contain an aldehyde group. These are called aldoses. Example: \[ \text{Glucose} \] Glucose is a polyhydroxy aldehyde.

Step 2: Understand polyhydroxy ketones.
Some sugars contain a ketone group. These are called ketoses. Example: \[ \text{Fructose} \] Fructose is a polyhydroxy ketone.

Step 3: Optical activity condition.
Many sugars are optically active because they contain chiral carbon atoms. However, the broad definition of sugars does not require every sugar-like compound to be optically active. Therefore, the safest and broadest definition is: \[ \text{polyhydroxy aldehydes or ketones which may or may not be optically active} \]

Step 4: Check the options.
Option (A) includes only aldehydes, so it is incomplete.
Option (B) includes only ketones, so it is incomplete.
Option (C) is close, but it unnecessarily requires optical activity.
Option (D) is the broadest and correct definition. Hence, the correct answer is: \[ \boxed{(D)} \]