Which of the following vitamins is essential for normal vision?

1. A

   Folic acid

   Folic acid claims to be the essential vitamin for normal vision, but it is actually a B complex vitamin crucial for DNA synthesis and red blood cell formation, not eyesight.

2. B

   Riboflavin

   Riboflavin claims to support normal vision, and while its deficiency can cause eye disorders like keratitis, it is primarily Vitamin B2 and not the principal vitamin directly essential for the visual cycle.

3. C

   Niacin

   Niacin claims to be the primary vitamin for vision, but it is Vitamin B3, which is important for cellular metabolism and nervous system function rather than the primary pigment of the eye.

4. D

   Retinol

   Retinol claims to be essential for normal vision, and this is the correct official key because retinol is an active form of Vitamin A, which forms rhodopsin, a pigment required for low-light and color vision, making it biologically indispensable for the human eye.

Summary. Official key is (d) Retinol is essential for normal vision. Vitamins are vital organic compounds needed in small quantities for various physiological functions in the human body. While B-complex vitamins like folic acid, riboflavin, and niacin play distinct roles in metabolism and cellular health, Vitamin A in the form of retinol specifically targets ocular health. Deficiency of retinol leads to night blindness and xerophthalmia, confirming its direct link to vision. Therefore, option (d) is the correct choice.