(A): When a sound source moves towards observer, then frequency of sound increases.
(R): Wavelength of sound in medium towards observer is decreased.

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 assertion and reasoning question, we need to analyze both statements carefully.

### Step 1: Analyze the Assertion
- **Assertion (A)**: "When a sound source moves towards an observer, then the frequency of sound increases."
- This statement is true. According to the Doppler effect, when a sound source approaches an observer, the sound waves get compressed, leading to an increase in frequency. The frequency is inversely related to the wavelength, and as the source moves closer, the waves reach the observer more frequently.

### Step 2: Analyze the Reasoning
- **Reason (R)**: "Wavelength of sound in the medium towards the observer is decreased."
- This statement is also true. As the sound source approaches the observer, the wavelength of the sound waves decreases. This is because the distance between successive wavefronts shortens as the source moves closer.

### Step 3: Determine the Relationship Between A and R
- While both statements are true, we need to determine if the reasoning (R) correctly explains the assertion (A).
- The assertion is explained by the fact that as the source moves towards the observer, the time period of the waves decreases, which leads to an increase in frequency. The reasoning about the wavelength decreasing is related but does not directly explain why the frequency increases.

### Conclusion
- Both the assertion and reasoning are true, but the reasoning does not correctly explain the assertion. Thus, the correct answer is that both statements are true, but the reasoning is not the correct explanation of the assertion.

### Final Answer
- Both assertion (A) and reasoning (R) are true, but R is not the correct explanation of A.

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