Give reason for the following:
Although hydrogen is lighter than air it cannot be collected by downward displacement of air.

Explanation

To answer the question, "Although hydrogen is lighter than air, it cannot be collected by downward displacement of air," we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Properties of Hydrogen**:
- Hydrogen is indeed lighter than air. The molecular weight of hydrogen (H₂) is about 2 g/mol, while the average molecular weight of air is approximately 29 g/mol.

2. **Definition of Downward Displacement of Air**:
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