(A): Apparent frequency is equal to actual frequency when there is no relative motion between source and observer.
(R): When there is no relative motion between the source and observer the velocity of sound is zero

Options

A. Both 'A' and 'R' are true and 'R' is the correct, explanation of 'A'.
B. Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
C. A' is true and 'R' is false
D. Both 'A' and 'R' are false

Answer

To solve the question regarding the assertion and reason statements, we will analyze both statements step by step.

### Step 1: Analyze the Assertion (A)
The assertion states: "Apparent frequency is equal to actual frequency when there is no relative motion between source and observer."

1. **Understanding Apparent Frequency**: Apparent frequency refers to the frequency of a wave as perceived by an observer, which can differ from the actual frequency emitted by the source due to relative motion.
2. **Condition of No Relative Motion**: When there is no relative motion between the source and the observer, the observer is at rest relative to the source.
3. **Conclusion on Assertion**: In this scenario, the apparent frequency (F') is equal to the actual frequency (F) because there is no Doppler effect influencing the frequency. Therefore, the assertion (A) is **true**.

### Step 2: Analyze the Reason (R)
The reason states: "When there is no relative motion between the source and observer, the velocity of sound is 0."

1. **Understanding Velocity of Sound**: The velocity of sound is a property of the medium through which it travels (e.g., air, water) and is not dependent on the motion of the source or observer.
2. **Condition of No Relative Motion**: Even if the source and observer are stationary relative to each other, sound can still propagate through the medium at its characteristic speed.
3. **Conclusion on Reason**: The statement that the velocity of sound is 0 when there is no relative motion is **false**. The sound still travels at its normal speed in the medium.

### Final Conclusion
- Assertion (A) is **true**.
- Reason (R) is **false**.

### Answer Selection
Based on the analysis, the correct option is: **A is true and R is false**.

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