Assertion : Newton's rings are formed in the reflected system. When the space between the lens and the glass plate is filled with a liquid of refractive index greater than that of glass, the central spot of the pattern is bright.
Reason : This is because the reflections in these cases will be from a denser to a rarer medium and the two interfering rays are reflected under similar conditions.

Options

A. If both Assertion `&` Reason are True `&` the Reason is a correct explanation of the Assertion.
B. If both Assertion `&` Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion `&` Reason are False.

Answer

To solve the question regarding Newton's rings and the assertion and reason provided, we can break down the problem step by step.

### Step-by-Step Solution:

1. **Understanding Newton's Rings**:
- Newton's rings are a pattern of concentric circles formed due to the interference of light waves reflected from the top surface of a convex lens and the flat glass plate beneath it.

2. **Assertion Analysis**:
- The assertion states that when the space between the lens and the glass plate is filled with a liquid of higher refractive index than glass, the central spot of the pattern is bright.
- This can be understood by recalling that the central spot is bright when there is constructive interference.

3. **Condition for Bright Central Spot**:
- For constructive interference to occur, the path difference between the two reflected rays must be an integral multiple of the wavelength.
- When light reflects from a medium of lower refractive index to a higher refractive index, a phase change of π (or half a wavelength) occurs. Conversely, when light reflects from a higher refractive index to a lower refractive index, there is no phase change.

4. **Filling with Liquid**:
- If the space is filled with a liquid of higher refractive index than glass, the reflection occurs from a denser medium (liquid) to a rarer medium (air).
- This means that there is no phase change upon reflection at the liquid-air interface, and thus the path difference remains conducive for constructive interference.

5. **Conclusion on Assertion**:
- Therefore, the assertion is correct: the central spot is bright when the space is filled with a liquid of refractive index greater than that of glass.

6. **Reason Analysis**:
- The reason states that reflections in these cases will be from a denser to a rarer medium and that the two interfering rays are reflected under similar conditions.
- This is also correct as explained above; the lack of phase change at the liquid-air boundary leads to constructive interference.

7. **Final Evaluation**:
- Both the assertion and reason are true, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason correctly explains the assertion.