Question

Assertion (A): D(+)-Glucose is dextrorotatory in nature.
Reason (R): (+) represents dextrorotatory nature and D represents its configuration.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

{Important Distinction:} D/L → Configuration (structure) (+)/(–) → Optical activity (experimentally observed) D does NOT always mean dextrorotatory.

Answer 1

The Correct Option is A

Concept: In carbohydrate chemistry, the symbols
D/L and
(+)/(–) have different meanings:

• 
  D/L notation → Refers to the
  configuration of the molecule relative to glyceraldehyde.
• 
  (+)/(–) notation → Refers to the
  optical rotation of plane-polarized light.

Step 1: Analyze Assertion (A). D(+)-Glucose means:

• D → Configuration similar to D-glyceraldehyde
• (+) → Rotates plane-polarized light to the right (dextrorotatory)

Hence, it is dextrorotatory. \(\Rightarrow\) Assertion is true.
Step 2: Analyze Reason (R). The reason states:

• (+) represents dextrorotation → Correct
• D represents configuration → Correct

This directly explains why D(+)-glucose is dextrorotatory.
Step 3: Logical connection. Since the reason correctly explains the assertion: \[ \therefore \text{Both A and R are true and R explains A} \]