(A): Under given conditions of pressure and temperature, sound travels faster in a monoatomic gas than in diatomic gas.
(R): Opposition for wave to travel is more in diatomic gas than monoatomic gas.

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 given assertion-reason question, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
The assertion states that under given conditions of pressure and temperature, sound travels faster in a monoatomic gas than in a diatomic gas.

- **Explanation**: The speed of sound in a gas is influenced by the molecular structure of the gas. Monoatomic gases (like helium or neon) consist of single atoms, while diatomic gases (like oxygen or nitrogen) consist of molecules made up of two atoms.

### Step 2: Understanding the Reason
The reason states that the opposition for a wave to travel is more in diatomic gas than in monoatomic gas.

- **Explanation**: The opposition to sound waves traveling through a medium can be related to the specific heat capacities of the gas. The adiabatic constant (γ = Cp/Cv) plays a crucial role in determining the speed of sound.

### Step 3: Relating the Concepts
The speed of sound in a gas can be expressed as:
\[ v = \sqrt{\frac{\gamma \cdot P}{\rho}} \]
where:
- \( v \) is the speed of sound,
- \( \gamma \) is the adiabatic constant,
- \( P \) is the pressure,
- \( \rho \) is the density of the gas.

For monoatomic gases, \( \gamma \) is approximately 1.66, while for diatomic gases, \( \gamma \) is approximately 1.4.

### Step 4: Comparing the Speeds
Since \( \gamma \) for monoatomic gases is greater than that for diatomic gases, the speed of sound in monoatomic gases will be greater than in diatomic gases when pressure and density are constant.

### Conclusion
Thus, the assertion is true: sound travels faster in monoatomic gases than in diatomic gases. However, the reason provided is not a valid explanation for the assertion, making it false.

### Final Answer
- **Assertion (A)**: True
- **Reason (R)**: False