Which of the following vitamins is essential for normal vision?

The correct answer is D) Retinol, which is Vitamin A. In the retina, 11-cis-retinal, derived from retinol, combines with the protein opsin to form rhodopsin, the pigment in rod cells that works in dim light. Without enough retinol, rhodopsin regeneration falls, causing night blindness (nyctalopia). Severe deficiency leads to xerophthalmia, Bitot's spots and keratomalacia.

• A) Folic acid (B9): Essential for DNA synthesis and neural tube closure in pregnancy. It has no direct role in the visual pigment cycle.
• B) Riboflavin (B2): A component of FMN and FAD coenzymes. Its deficiency gives angular stomatitis, cheilosis and glossitis, not a specific visual disorder.
• C) Niacin (B3): Deficiency causes pellagra, marked by dermatitis, diarrhoea and dementia.

For Mains, this links to malnutrition and public health. Vitamin A prophylaxis under the National Health Mission and the wider nutrition programmes address night blindness among young children and pregnant women.

Trap: Students confuse retinol with retinal or beta-carotene. Beta-carotene is only a provitamin A, and the question asks for the vitamin itself.