Recall the classification of vitamins

Vitamins are broadly classified into:

• Fat-soluble vitamins: $A, D, E, K$
• Water-soluble vitamins: $B$-complex and $C$

Check each option

• A: Vitamin D
  Vitamin $D$ is fat-soluble.

• B: Vitamin E
  Vitamin $E$ is fat-soluble.

• C: Vitamin K
  Vitamin $K$ is fat-soluble.

• D: Vitamin C
  Vitamin $C$ is water-soluble.

Identify the correct option

Therefore, the water-soluble vitamin among the given options is: $\boxed{\text{Vitamin C}}$

Comparison with stored correct answer

The stored correct answer is D, which corresponds to Vitamin C. This matches the derived answer.