Which is the lightest gas ?

Options

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

Answer

To determine which is the lightest gas among the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Gases**: The question presents four gases: Nitrogen (N), Hydrogen (H), Helium (He), and Oxygen (O).

2. **Find the Atomic Numbers**:
- Nitrogen (N) has an atomic number of 7.
- Hydrogen (H) has an atomic number of 1.
- Helium (He) has an atomic number of 2.
- Oxygen (O) has an atomic number of 8.

3. **Compare the Atomic Numbers**:
- We need to compare the atomic numbers to determine which gas is the lightest. The atomic number gives us an idea of the mass of the element; the lower the atomic number, the lighter the gas.
- Comparing the atomic numbers:
- Hydrogen (1) < Helium (2) < Nitrogen (7) < Oxygen (8)

4. **Conclusion**:
- Since Hydrogen has the lowest atomic number (1), it is the lightest gas among the options provided.

5. **Final Answer**:
- Therefore, the lightest gas is **Hydrogen (H)**.