If liquefied oxygen at 1 atmospheric pressure is heated from 50K to 300k by supplying heat at constant rate. The graph of temperature vs time will be

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Explanation

To solve the problem of how the temperature of liquefied oxygen changes over time when heated at a constant rate from 50 K to 300 K, we can break it down into several steps:

### Step-by-Step Solution:

1. **Identify the Initial and Final States**:
- The initial temperature of liquefied oxygen is 50 K.
- The final temperature is 300 K.

2. **Determine the Boiling Point of Oxygen**:
- The boiling point of oxygen is approximately 90 K. This is a crucial point where the state of the substance will change from liquid to gas.

3. **Heating the Liquid Oxygen**:
- As the oxygen is heated from 50 K to 90 K, the temperature will increase steadily. This portion of the graph will be a straight line as the temperature rises with time.

4. **Phase Change at the Boiling Point**:
- At 90 K, the oxygen will start to boil. During the phase change from liquid to gas, the temperature will remain constant at 90 K until all the liquid has converted to gas. This will be represented as a horizontal line on the graph (time will continue to pass, but temperature will not change).

5. **Heating the Gaseous Oxygen**:
- After the phase change is complete, the temperature of the gaseous oxygen will begin to increase again. This will continue until it reaches 300 K. This portion of the graph will again be a straight line, indicating a steady increase in temperature with time.

6. **Graphing Temperature vs. Time**:
- The graph will consist of three distinct sections:
- A rising line from 50 K to 90 K (liquid phase).
- A horizontal line at 90 K (phase change).
- Another rising line from 90 K to 300 K (gas phase).

### Final Graph Description:
- The y-axis represents temperature, and the x-axis represents time.
- The graph starts at 50 K, rises to 90 K, remains flat at 90 K during the phase change, and then rises again to 300 K.

### Conclusion:
The correct graph for the temperature versus time will have a linear increase from 50 K to 90 K, a flat line at 90 K, and another linear increase from 90 K to 300 K.