Assertion. The temperature of a gas does not change when it undergoes an adiabatic expansion.
Reason . During an adiabatic expansion of a real gas, the internal energy of the gas remains constant.

Options

A. If both A and R are true,andR is the true explanation of A.
B. If both A and R are true,but R is not the true explanation of A.
C. If A is true, but R is false
D. If both A and R are false.

Answer

To analyze the assertion and reason provided in the question, we need to understand the concepts of adiabatic processes and internal energy in thermodynamics.

### Step-by-step Solution:

1. **Understanding Adiabatic Expansion**:
- An adiabatic process is one in which no heat is exchanged with the surroundings (Q = 0). This means that any change in the internal energy of the gas must come from work done on or by the gas.

2. **Internal Energy and Work Done**:
- For an ideal gas undergoing an adiabatic expansion, the change in internal energy (ΔU) is equal to the work done (W) on the gas. This can be expressed as:
\[ \Delta U = W \]
- In an adiabatic expansion, the gas does work on the surroundings, which means that the internal energy decreases, leading to a drop in temperature.

3. **Assertion Analysis**:
- The assertion states that "the temperature of a gas does not change when it undergoes an adiabatic expansion." This is incorrect because, during an adiabatic expansion, the gas does work, and since no heat is added, the internal energy decreases, resulting in a decrease in temperature.

4. **Reason Analysis**:
- The reason states that "during an adiabatic expansion of a real gas, the internal energy of the gas remains constant." This is also incorrect. In an adiabatic expansion, the internal energy does not remain constant; it decreases as the gas does work on the surroundings.

5. **Conclusion**:
- Both the assertion and the reason are false. The temperature of a gas does change during an adiabatic expansion, and the internal energy does not remain constant.

### Final Answer:
Both the assertion and the reason are false.