The letter ‘D’ in carbohydrates signifies
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Configuration
In carbohydrates the reference is glyceraldehyde: a sugar is D if the –OH on its lowest chiral carbon (the one farthest from the carbonyl group) is on the right in the Fischer projection, as in (+)-glyceraldehyde. For example, D-(+)-glucose and D-(−)-fructose are both D sugars although they rotate light in opposite directions.
Why the other options are incorrect
Option (1) Dextrorotatory — Incorrect. The direction of rotation is shown by (+) or d, not by D; D-fructose is laevorotatory.
Option (3) Diamagnetic character — Incorrect. This is a magnetic property, unrelated to the D/L notation.
Option (4) Optical activity — Incorrect. D and L have no relation with whether or how a compound rotates plane polarised light.
NCERT (2026-27 edition):
Glucose – …
