Adaptation of eyes in dark is due to
(a) Depletion of visual pigments in rods
(b) Depletion of visual pigments in cones
(c) Repletion of visual pigments in cones
(d) Repletion of visual pigments in rods

Options

A. Depletion of visual pigments in rods
B. Depletion of visula pigments in cones
C. Repletion of visual pigments in cones
D. Repletion of visual pigments in rods.

Answer

To solve the question regarding the adaptation of eyes in the dark, we need to analyze the options provided and understand the role of visual pigments in rods and cones.

### Step-by-Step Solution:

1. **Understanding Eye Adaptation**:
- Eye adaptation refers to the ability of the eyes to adjust to varying levels of light. This can occur in both bright and dark environments.

2. **Identifying Key Players**:
- The main components involved in the adaptation of the eyes are the pupil, rods, and cones.
- The pupil regulates the amount of light entering the eye, but it does not play a significant role in adaptation to darkness.

3. **Role of Rods and Cones**:
- Cones are responsible for color vision and function best in bright light. They are not primarily involved in dark adaptation.
- Rods, on the other hand, are responsible for vision in low light conditions (black and white vision) and are crucial for adapting to darkness.

4. **Visual Pigments**:
- Both rods and cones contain visual pigments. The pigment in rods is called rhodopsin.
- In dark conditions, the visual pigments in rods need to regenerate (repletion) to allow for better sensitivity to light.

5. **Analyzing the Options**:
- (a) Depletion of visual pigments in rods: Incorrect, as depletion would hinder adaptation.
- (b) Depletion of visual pigments in cones: Incorrect, as cones are not primarily involved in dark adaptation.
- (c) Repletion of visual pigments in cones: Incorrect, as cones do not play a significant role in dark adaptation.
- (d) Repletion of visual pigments in rods: Correct, as the regeneration of rhodopsin in rods is essential for adapting to darkness.

6. **Conclusion**:
- The correct answer is (d) Repletion of visual pigments in rods, as this process is crucial for the adaptation of the eyes in dark conditions.

### Final Answer:
**(d) Repletion of visual pigments in rods**