It is present in rod cells and useful in night vision:

Options

A. Vitamin K
B. melanin
C. rhodopsin
D. vitamin C

Answer

To solve the question "It is present in rod cells and useful in night vision," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components of Rod Cells**:
- Rod cells are photoreceptor cells located in the retina of the eye. They are responsible for vision in low light conditions.

2. **Understand the Function of Rod Cells**:
- Rod cells are primarily responsible for night vision (scotopic vision). They are sensitive to light and allow us to see in dim lighting.

3. **Recognize Key Pigments in Rod Cells**:
- The main pigment found in rod cells is called rhodopsin. It is a light-sensitive receptor protein.

4. **Evaluate the Options Given**:
- The options provided are:
1. Vitamin K
2. Melanin
3. Rhodopsin
- Vitamin K is involved in blood clotting and is not related to vision. Melanin is a pigment that provides color to the skin, hair, and eyes but does not play a role in night vision.

5. **Confirm the Correct Answer**:
- Since rhodopsin is specifically mentioned as being present in rod cells and is crucial for night vision, the correct answer is option 3: Rhodopsin.

### Final Answer:
The correct answer is **3. Rhodopsin**.

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