Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Explanation

To find the number of neutrons in a helium atom with an atomic mass of 4 u and 2 protons, we can follow these steps:

### Step-by-Step Solution

1. **Understand the Definitions**:
- Atomic mass (A) is the total number of protons and neutrons in the nucleus of an atom.
- The number of protons (Z) is the atomic number of the element.

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