The gas which turns into liquid at the lowest temperature among the following is -

Options

A. Hydrogen
B. Oxygen
C. Helium
D. Nitrogen

Answer

To determine which gas turns into a liquid at the lowest temperature, we need to analyze the molecular weights of the gases provided in the options. The gas with the lowest molecular weight will require the least temperature for liquefaction.

### Step-by-Step Solution:

1. **Understand the Concept of Liquefaction**:
- Liquefaction is the process where a gas turns into a liquid. The temperature at which this occurs varies depending on the molecular weight of the gas.

2. **Identify the Relationship Between Molecular Weight and Liquefaction Temperature**:
- Generally, gases with lower molecular weights liquefy at lower temperatures compared to gases with higher molecular weights. This means that the heavier the molecule, the higher the temperature required for liquefaction.

3. **List the Gases and Their Molecular Weights**:
- Let's consider the gases mentioned in the options:
- **Hydrogen (H2)**: Atomic weight of H = 1, so molecular weight of H2 = 2.
- **Oxygen (O2)**: Atomic weight of O = 16, so molecular weight of O2 = 32.
- **Helium (He)**: Atomic weight of He = 4, so molecular weight of He = 4.
- **Nitrogen (N2)**: Atomic weight of N = 14, so molecular weight of N2 = 28.

4. **Compare the Molecular Weights**:
- Now we compare the molecular weights:
- Hydrogen: 2
- Helium: 4
- Nitrogen: 28
- Oxygen: 32
- Among these, Hydrogen has the lowest molecular weight.

5. **Conclusion**:
- Since Hydrogen has the lowest molecular weight, it will require the least temperature for liquefaction. Therefore, the gas that turns into liquid at the lowest temperature among the given options is **Hydrogen**.

### Final Answer:
The gas which turns into liquid at the lowest temperature among the following is **Hydrogen**.

---