Assertion : A physical quantity which has zero dimension may have unit of measurement.
Reason : Two physical entities having same dimensional formula may have different units of measurement.

Options

A. If both assertion and reason are correct and reason is a correct explanation of the assertion.
B. If both assertion and reason are correct and reason is not the correct explanation of the assertion.
C. If assertion is correct but reason is incorrect.
D. If assertion is incorrect but reason is correct.

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts step by step.

### Step 1: Understanding the Assertion
The assertion states that a physical quantity which has zero dimension may have a unit of measurement.

- **Zero Dimension**: A physical quantity with zero dimension means that it is dimensionless. An example of this is an angle, which can be expressed in radians.

**Conclusion**: The assertion is true because angles are dimensionless but still have a unit of measurement (radians).

### Step 2: Understanding the Reason
The reason states that two physical entities having the same dimensional formula may have different units of measurement.

- **Dimensional Formula**: This refers to the expression that shows how a physical quantity can be expressed in terms of fundamental dimensions (mass, length, time, etc.). For example, both energy (in joules) and torque (in Newton-meters) have the same dimensional formula (ML²T⁻²).

**Conclusion**: The reason is also true because different physical quantities can share the same dimensional formula but still be measured in different units.

### Step 3: Evaluating the Relationship
Now, we need to evaluate whether the reason provided is a correct explanation for the assertion.

- The assertion is about a dimensionless quantity having a unit of measurement, while the reason discusses different units for quantities that share the same dimensional formula.

**Conclusion**: Although both the assertion and the reason are true, the reason does not explain the assertion. The assertion is about dimensionless quantities like angles, while the reason refers to quantities that may or may not be dimensionless.

### Final Conclusion
Both the assertion and the reason are correct, but the reason does not serve as a correct explanation for the assertion.

### Answer:
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason is not the correct explanation of the assertion.

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