A : The propagation of sound in air should be an isothermal process .
R : As air is bad conductor of heat , its temperature does not change by compression or expansion.

Answer

To analyze the given statements about the propagation of sound in air, we need to evaluate both the assertion (A) and the reason (R) provided in the question.

### Step 1: Understand the Assertion (A)
The assertion states that "the propagation of sound in air should be an isothermal process." An isothermal process is one in which the temperature remains constant throughout the process.

**Hint:** Recall the definition of isothermal processes and consider whether sound propagation can maintain a constant temperature.

### Step 2: Evaluate the Assertion
The assertion is incorrect. The propagation of sound in air is not an isothermal process. Instead, it is an adiabatic process. In an adiabatic process, there is no heat exchange with the surroundings, and the temperature can change due to compression and rarefaction of air.

**Hint:** Think about how sound waves create regions of compression and rarefaction and how this affects temperature.

### Step 3: Understand the Reason (R)
The reason states that "as air is a bad conductor of heat, its temperature does not change by compression or expansion."

**Hint:** Consider the properties of air as a medium and how heat conduction affects temperature during sound propagation.

### Step 4: Evaluate the Reason
This reason is also incorrect. While it is true that air is a poor conductor of heat, the temperature can still change during the compression and rarefaction of sound waves. The process of sound propagation involves rapid changes in pressure, leading to changes in temperature, which contradicts the assertion that temperature remains constant.

**Hint:** Reflect on the physical principles of sound waves and how they interact with the medium.

### Step 5: Conclusion
Since both the assertion (A) and the reason (R) are incorrect, the final conclusion is that neither statement holds true.

**Final Answer:** Both A and R are incorrect.