The noble gas which shown abnormal behaviour in liquid state and behaves as a super fluid is ____.

Explanation

To solve the question regarding which noble gas shows abnormal behavior in the liquid state and behaves as a superfluid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Noble Gases**: First, we need to recall the noble gases, which include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

2. **Focus on Liquid State Behavior**: The question specifically asks about the behavior of these gases in their liquid state. Among these gases, Helium is known for its unique properties when it is cooled to a liquid state.

3. **Cooling Helium**: When helium is cooled below 4.18 Kelvin, it transitions into a liquid state. Further cooling to around 2.2 Kelvin results in the formation of a specific phase of liquid helium known as Helium II.

4. **Characteristics of Liquid Helium**: Liquid helium exhibits abnormal behavior:
- It flows without any friction, which is not typical for ordinary liquids.
- It has a discontinuity in heat capacity, meaning its heat capacity can change abruptly.
- It has a very low density and is considered to have zero viscosity.

5. **Definition of Superfluid**: Due to these characteristics, liquid helium is classified as a superfluid. Superfluids are known for their ability to flow without viscosity and exhibit other unusual properties.

6. **Conclusion**: Based on the above points, the noble gas that shows abnormal behavior in the liquid state and behaves as a superfluid is **Helium**.

### Final Answer:
The noble gas which shows abnormal behavior in liquid state and behaves as a superfluid is **Helium**.

---