Assertion : According to Newton's law, good conductors of elctricity are also conductors of heat.
Reason : At a given temperature , `e_(lambda) prop a_(lambda)` for any body.

Options

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

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
The assertion states that "According to Newton's law, good conductors of electricity are also conductors of heat." We need to determine if this statement is true or false.

2. **Evaluating the Assertion**:
Newton's law primarily deals with cooling and does not explicitly state that good conductors of electricity are necessarily good conductors of heat. While it is often observed that materials that conduct electricity well (like metals) also conduct heat well, this is not a universal law stated by Newton. Therefore, the assertion is **false**.

3. **Understanding the Reason**:
The reason states that "At a given temperature, \( e_{\lambda} \propto a_{\lambda} \) for any body." Here, \( e_{\lambda} \) refers to the emissivity of a body, and \( a_{\lambda} \) refers to its absorptive power. This relationship is indeed true and is known as Kirchhoff's law of thermal radiation, which states that at thermal equilibrium, the emissivity of a body is equal to its absorptive power.

4. **Evaluating the Reason**:
Since the reason is a true statement in thermodynamics, we conclude that the reason is **true**.

5. **Final Conclusion**:
Since the assertion is false and the reason is true, we can summarize our findings:
- Assertion: **False**
- Reason: **True**

Thus, the correct answer is that the assertion is false while the reason is true.