Define isotopes why do isotopes have same atomic number but differente mass numbers? Explain with the help an example.

Explanation

### Step-by-Step Solution:

1. **Definition of Isotopes**:
- Isotopes are forms of the same element that have the same number of protons but different numbers of neutrons. This results in different mass numbers for each isotope.

2. **Understanding Atomic Number**:
- The atomic number of an element is defined as the number of protons in the nucleus of an atom. Since isotopes of an element have the same number of protons, they share the same atomic number.

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