What is understood by 'hydrogen gap'?

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept of Hydrogen Gap**:
- The hydrogen gap refers to a specific phenomenon in the periodic table related to the formation of hydrides. Hydrides are compounds formed when hydrogen combines with other elements.

2. **Hydrides Formation**:
- Hydrogen can combine with less electronegative elements to form various types of hydrides. Examples include:
- Water (H₂O)
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