An ideal gas is filled in a vessel, then

Options

A. If it is placed inside a moving train, its temperature increases
B. Its centre of mass moves randomly
C. Its temperature remains constant in a moving car
D. None of these

Explanation

To solve the question regarding the behavior of an ideal gas in a vessel when placed in a moving train or car, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Behavior of Gases**:
- An ideal gas consists of molecules that are in constant random motion. The temperature of a gas is directly related to the average kinetic energy of its molecules.

2. **Analyzing Option A**:
- Option A states that if the gas-filled vessel is placed inside a moving train, its temperature increases.
- **Analysis**: The motion of the train does not affect the random motion of the gas molecules inside the vessel. The temperature of the gas depends on the kinetic energy of its molecules, which remains constant if no heat is added or removed. Therefore, this option is incorrect.

3. **Analyzing Option B**:
- Option B states that the center of mass of the gas moves randomly.
- **Analysis**: The center of mass of the gas molecules will not move randomly in the context of the vessel being in a moving train. The gas molecules will continue their random motion relative to the vessel, but the overall center of mass of the gas in the vessel remains stationary relative to the vessel itself. Thus, this option is also incorrect.

4. **Analyzing Option C**:
- Option C states that the temperature remains constant in a moving car.
- **Analysis**: Similar to the case with the moving train, the temperature of the gas in the vessel will remain constant as long as there is no heat exchange with the environment. The motion of the car does not influence the internal kinetic energy of the gas molecules. Therefore, this option is correct.

5. **Analyzing Option D**:
- Option D states "none of this."
- **Analysis**: Since we have determined that option C is correct, option D is incorrect.

### Conclusion:
The correct answer is **Option C**: The temperature remains constant in a moving car.

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