If is present in rod cells and useful in night vision `,`

Options

A. Melanin
B. Rhodopsin
C. Vitamin C
D. Vitamin K

Answer

### Step-by-Step Solution

1. **Identify the Components of the Question**: The question asks for a substance that is present in rod cells and is useful for night vision.

2. **Examine the Options**: The options provided are:
- A) Melanin
- B) Rhodopsin
- C) Vitamin C
- D) Vitamin K

3. **Analyze Each Option**:
- **Option A: Melanin**: Melanin is a pigment found in the skin that is responsible for skin color and protection against UV radiation. It is not involved in night vision and is not present in rod cells.
- **Option B: Rhodopsin**: Rhodopsin is a photopigment found in rod cells of the retina. It is crucial for vision in low-light conditions (night vision) as it is sensitive to light.
- **Option C: Vitamin C**: Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that is important for various bodily functions, but it is not present in rod cells and does not play a role in night vision.
- **Option D: Vitamin K**: Vitamin K is a fat-soluble vitamin mainly involved in blood clotting. It is not related to vision and is not found in rod cells.

4. **Determine the Correct Answer**: Based on the analysis, the correct answer is **Option B: Rhodopsin**, as it is the only substance that is present in rod cells and is essential for night vision.

5. **Final Conclusion**: The substance present in rod cells that is useful for night vision is **Rhodopsin**.