Assertion (A): `chi-T` graph for a diamagnetic material is a straight line parallel to `T-`axis
Reason (R ): This is because susceptibility of a diamagnetic material is not affected by temperature

Options

A. If both Assertain and Reason are true and Reason is the correct explanation of Assertain
B. If both Assertain and Reason are true but Reason is not correct explantion of Assertain
C. If Assertion is true but Reason is false
D. If Assertion is false but Reason in true.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the `chi-T` graph (susceptibility vs. temperature graph) for a diamagnetic material is a straight line parallel to the T-axis.
- This implies that the susceptibility (χ) remains constant as the temperature (T) changes.

2. **Understanding the Reason (R)**:
- The reason given is that the susceptibility of a diamagnetic material is not affected by temperature.
- This means that regardless of the temperature, the susceptibility remains the same for diamagnetic materials.

3. **Analyzing Diamagnetic Materials**:
- Diamagnetic materials exhibit a very weak negative susceptibility.
- According to the principles of magnetism, the susceptibility of diamagnetic materials is indeed constant and does not vary with temperature.

4. **Graphical Representation**:
- If we plot susceptibility (χ) on the y-axis and temperature (T) on the x-axis, since χ is constant for a diamagnetic material, the graph will be a horizontal line parallel to the T-axis.
- This confirms that the assertion is correct.

5. **Conclusion**:
- Both the assertion (A) and the reason (R) are true.
- Additionally, the reason provided correctly explains the assertion.

### Final Answer:
- Both the assertion and the reason are true, and the reason is the correct explanation for the assertion.

---