(A): Compression and rarefaction involve changes in pressure.
(R): When particles are compressed, density of medium increases and when they are rarefied, density of medium decreases

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, we need to analyze both the assertion (A) and the reason (R) provided, and determine their truth values and whether R correctly explains A.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "Compression and rarefaction involve changes in pressure."
- In the context of waves, particularly longitudinal waves, compression refers to areas where particles are closer together, resulting in higher pressure. Conversely, rarefaction refers to areas where particles are spread apart, leading to lower pressure.
- Therefore, this assertion is **true**.

2. **Understanding the Reason (R)**:
- The reason states: "When particles are compressed, density of medium increases and when they are rarefied, density of medium decreases."
- In compression, particles are indeed closer together, which increases the density of the medium. In rarefaction, particles are farther apart, resulting in a decrease in density.
- Thus, this reason is also **true**.

3. **Checking if R is the Correct Explanation of A**:
- The assertion (A) is about changes in pressure due to compression and rarefaction.
- The reason (R) explains how density changes in these regions, which directly affects pressure (higher density leads to higher pressure and lower density leads to lower pressure).
- Since R accurately explains the mechanism behind A, we conclude that R is the correct explanation of A.

4. **Final Conclusion**:
- Both A and R are true, and R is the correct explanation of A. Therefore, the correct option is:
- **Option 1: Both A and R are true and R is the correct explanation of A.**