Assertion: Weston is a standard cell.
Reason: its e.m.f. does not change with temperature.

Options

A. if both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false
D. If the assertion and reason both are false.

Explanation

To analyze the given assertion and reason, we will break it down step by step.

### Step 1: Understand the Assertion
The assertion states that "Weston is a standard cell."
- A standard cell is a reference cell with a known and stable electromotive force (e.m.f.) used for calibration and measurement purposes in electrochemistry.

### Step 2: Understand the Reason
The reason provided is "its e.m.f. does not change with temperature."
- The e.m.f. of a cell is influenced by various factors, including temperature. However, the Weston cell is designed to maintain a stable e.m.f. over a range of temperatures, making it reliable for standard measurements.

### Step 3: Evaluate the Relationship
Now we need to determine if the reason correctly explains the assertion.
- The assertion is true: the Weston cell is indeed a standard cell.
- The reason is also true: the e.m.f. of the Weston cell does not significantly change with temperature, which is one of the reasons it is used as a standard cell.

### Step 4: Conclusion
Since both the assertion and the reason are true, and the reason provides a valid explanation for the assertion, we conclude that:
- **Both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.**

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

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