## Core Concept
The question tests the knowledge of vitamins and their roles as antioxidants. Antioxidants are substances that can prevent or slow damage to cells caused by free radicals, unstable molecules that the body produces as a reaction to environmental and other pressures. They are often vitamins, minerals, or other nutrients.

## Why the Correct Answer is Right
Vitamin E is known for its role as an antioxidant in the body. It helps protect cells from damage caused by free radicals, which are unstable molecules that can harm cells. Vitamin E does this by stopping the production of free radicals, thereby preventing cell damage. This function makes it crucial for maintaining healthy skin, eyes, and immune function.

## Why Each Wrong Option is Incorrect
- **Option A:** Vitamin A, while important for vision, immune function, and reproduction, is not primarily known as an antioxidant, although it does have some antioxidant properties. Its primary roles do not classify it as an antioxidant vitamin in the same category as Vitamin E.
- **Option B:** Vitamin D is crucial for bone health and immune function but does not function as an antioxidant.
- **Option C:** Vitamin K is essential for blood clotting and bone health but is not classified as an antioxidant.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Vitamin E is often cited as a classic antioxidant vitamin. A helpful mnemonic could be "E for Eyes and Epidermis" highlighting its protective roles, but specifically, its antioxidant properties make it stand out.

## Correct Answer Line
**Correct Answer: C. Vitamin E.**