Liquid helium is called super fluid. Why? 

Explanation

**Step-by-Step Solution:**

1. **Understanding Liquid Helium**: Liquid helium is a unique state of matter that occurs when helium is cooled to very low temperatures.

2. **Critical Temperature**: When helium is cooled to a critical temperature of approximately 2.17 Kelvin, it undergoes a significant change in its physical properties.

3. **Discontinuity in Heat Capacity**: At this critical temperature, a remarkable discontinuity in heat capacity is observed. This means that the amount of heat required to change the temperature of the liquid helium changes abruptly.

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