`CO_2` is stored as a liquid in cylinder at:

Options

A. high pressure
B. low pressure
C. high temperature
D. low temperature

Explanation

To determine at what conditions CO₂ is stored as a liquid in a cylinder, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the State of CO₂**:
- Carbon dioxide (CO₂) is a gas at room temperature and atmospheric pressure.

2. **Need for Compression**:
- To store CO₂ in liquid form, we need to change its state from gas to liquid. This requires compressing the gas.

3. **Effect of Pressure**:
- When we compress a gas, we increase the pressure. Increasing the pressure causes the gas particles to come closer together, which can lead to a phase change from gas to liquid.

4. **Temperature Considerations**:
- CO₂ can exist as a liquid at certain temperatures, but to maintain it in liquid form, it is essential to apply high pressure.

5. **Conclusion**:
- Therefore, CO₂ is stored as a liquid in a cylinder at **high pressure**. This allows the gas to be compressed into a smaller volume and remain in liquid form.

### Final Answer:
CO₂ is stored as a liquid in a cylinder at **high pressure**.

---