Which isotope of hydrogen is known as ordinary hydrogen?

Explanation

To solve the question "Which isotope of hydrogen is known as ordinary hydrogen?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Isotopes**:
- Isotopes are variants of a chemical element that have the same number of protons (atomic number) but different numbers of neutrons, leading to different mass numbers.

2. **Identify the Isotopes of Hydrogen**:
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