Assertion:- The image focus (`2^(nd)` focus) and the object focus (`1^(st)` focus) are on the oppostie side of the biconvex or biconcave lens.
Reason:- The radii of curvature of a biconvex lens and biconcave lens are on the opposite side of the lens.

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, we need to analyze both the assertion and the reason provided.

### Step 1: Understanding the Assertion
The assertion states that the image focus (2nd focus) and the object focus (1st focus) are on opposite sides of the biconvex or biconcave lens.

- **Biconvex Lens**: For a biconvex lens, parallel rays of light converge to a point on the opposite side of the lens, which is the 2nd focus. The 1st focus is on the same side as the object.
- **Biconcave Lens**: For a biconcave lens, parallel rays diverge, and the 2nd focus is virtual and located on the same side as the object, while the 1st focus is on the opposite side.

Thus, the assertion is correct for biconvex lenses, but for biconcave lenses, the focuses are not on opposite sides.

### Step 2: Understanding the Reason
The reason states that the radii of curvature of a biconvex lens and a biconcave lens are on opposite sides of the lens.

- **Biconvex Lens**: The radii of curvature are positive, indicating that the curvature is outward.
- **Biconcave Lens**: The radii of curvature are negative, indicating that the curvature is inward.

This statement is also correct, as it accurately describes the nature of the radii of curvature for both types of lenses.

### Step 3: Evaluating the Relationship Between Assertion and Reason
While both the assertion and reason are true, the reason does not adequately explain the assertion. The focus of a lens is determined not only by the radii of curvature but also by the refractive index of the lens material and the surrounding medium.

### Conclusion
Based on the analysis:
- The assertion is true.
- The reason is true.
- However, the reason does not correctly explain the assertion.

Thus, the correct answer is: **Assertion and reason are true, but the reason is not a correct explanation of the assertion.**