A: The resolving power of a telescope decreases on decreasing the aperture of its objective lens.
R: The resolving power of a telescope is given as `D/(1.22 lamda)` where D is aperture of the objective and `lamda` is the wavelength of light.

Options

A. IF both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark(2)
C. IF Assertion is true statement but Reason is false then mark(3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the assertion and reason question, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Understand the Assertion
The assertion states that "the resolving power of a telescope decreases on decreasing the aperture of its objective lens."

**Explanation:**
- The resolving power of a telescope refers to its ability to distinguish between two closely spaced objects. A higher resolving power means that the telescope can distinguish finer details.
- The aperture of the objective lens is the diameter of the lens through which light enters the telescope. A larger aperture allows more light to enter and improves the telescope's ability to resolve details.

### Step 2: Understand the Reason
The reason states that "the resolving power of a telescope is given as D/(1.22 λ)," where D is the aperture of the objective and λ is the wavelength of light.

**Explanation:**
- The formula for resolving power (RP) is given by \( RP = \frac{D}{1.22 \lambda} \).
- Here, D is directly proportional to the resolving power. This means that as D increases, the resolving power increases, and conversely, as D decreases, the resolving power decreases.

### Step 3: Analyze the Relationship
From the formula \( RP = \frac{D}{1.22 \lambda} \):
- If the aperture D decreases, the value of the resolving power RP will also decrease, since λ (wavelength) remains constant for a given light source.

### Step 4: Conclusion
Both the assertion and the reason are true:
- The assertion is true because decreasing the aperture leads to a decrease in resolving power.
- The reason is also true as it correctly describes the relationship between the aperture and the resolving power.

### Final Answer
Both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion.