A vitamin that serves as an intracellular antioxidant.

A vitamin that serves as an intracellular antioxidant.

• A. Vit. D
• B. Vit. A
• C. Vit. K
• D. Vit. E

Answer: (D)

Antioxidants protect cellular components from oxidative damage, and the one that acts inside membranes is vitamin E. It is lipid-soluble and resides within cell membranes, where it donates a hydrogen atom to lipid radicals. This stops the chain reactions of lipid peroxidation, keeping membrane integrity intact. That intracellular, membrane-protecting role is what makes vitamin E the best answer.

The other vitamins have different primary roles: vitamin D helps regulate calcium and bone health; vitamin A supports vision and immune function; vitamin K is essential for blood clotting. While some can have minor antioxidant effects in other contexts, none are as classically described as intracellular membrane antioxidants as vitamin E.