Isotopes of an element differ in the number of ………in their nuclei

Explanation

To solve the question regarding isotopes of an element and what they differ in, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Isotopes**:
- Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.

2. **Identifying Components of the Nucleus**:
...