A : To increase the resolving power of a microscope, .oil immersion objective. can be used.
R : Resolving power of the microscope is given by the reciprocal of the maximum separation of two objects distinctly seen.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true and R is not the correct explanation of A
C. A is true and R is false
D. Both A and R are false

Answer

To solve the question regarding the assertion (A) and reason (R) related to the resolving power of a microscope, we will analyze both statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "To increase the resolving power of a microscope, oil immersion objective can be used."
- The resolving power of a microscope is the ability to distinguish between two closely spaced objects. Using an oil immersion objective improves this ability because oil has a higher refractive index than air.

**Hint**: Think about how the refractive index affects light's behavior in different media.

2. **Understanding the Reason (R)**:
- The reason states: "Resolving power of the microscope is given by the reciprocal of the maximum separation of two objects distinctly seen."
- This is a true statement. The resolving power (RP) can be mathematically expressed as RP = 1/d, where d is the minimum distance between two points that can be distinguished as separate.

**Hint**: Recall the formula for resolving power and how it relates to the distance between objects.

3. **Analyzing the Relationship**:
- The assertion is true because using an oil immersion objective increases the resolving power due to the higher refractive index of oil compared to air.
- The reason is also true and correctly explains the assertion, as it defines resolving power in terms of the separation distance.

**Hint**: Consider how both statements connect logically—does one explain the other?

4. **Conclusion**:
- Since both the assertion and reason are true, and the reason correctly explains the assertion, we conclude that the correct option is: "Both A and R are true, and R is the correct explanation of A."

**Hint**: Look for options that state both statements are true and check if the reason supports the assertion.

### Final Answer:
Both A and R are true, and R is the correct explanation of A.