A :Alloys of metals usually have greater resistivity than that of their constituent metals.
R : Alloys usually have much lower thermal coefficient of resistance than pure metals.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion then mark.
C. If Assertion is ture statement but Reason is false , then mark
D. If both Assertion and Reason are false statements then mark.

Answer

To analyze the given statements, we need to evaluate both the Assertion (A) and the Reason (R) provided in the question.

### Step 1: Understand the Assertion (A)
The assertion states that "Alloys of metals usually have greater resistivity than that of their constituent metals."

- **Explanation**: Alloys are mixtures of two or more metals. When metals are combined to form an alloy, the atomic structure is altered, leading to increased lattice distortion. This distortion disrupts the regular arrangement of atoms, which increases the scattering of charge carriers (electrons), resulting in higher resistivity compared to the pure metals that make up the alloy.

### Step 2: Understand the Reason (R)
The reason states that "Alloys usually have much lower thermal coefficient of resistance than pure metals."

- **Explanation**: The thermal coefficient of resistance indicates how much the resistance of a material changes with temperature. Alloys tend to have a lower thermal coefficient of resistance because their structure is less sensitive to temperature changes compared to pure metals. This means that as temperature increases, the resistance of alloys does not increase as significantly as that of pure metals.

### Step 3: Analyze the Relationship Between A and R
Now, we need to determine if the reason (R) justifies the assertion (A).

- The assertion (A) is true because alloys generally do have greater resistivity due to increased scattering mechanisms.
- The reason (R) is also true, as alloys do exhibit a lower thermal coefficient of resistance. However, it does not directly explain why alloys have greater resistivity. The reason discusses the temperature dependence of resistance rather than the inherent resistivity of the materials.

### Conclusion
- **Assertion (A)**: True
- **Reason (R)**: True
- **Justification**: The reason does not justify the assertion; therefore, while both statements are true, the reason does not explain the assertion.

### Final Answer
- A is true, R is true, but R is not the correct explanation for A.