An element belongs to group 17 and period 3 of the periodic table. Write the following:
The number of valence electrons in its atom.

Explanation

To determine the number of valence electrons in an element that belongs to Group 17 and Period 3 of the periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group and Period**:
- The element is in Group 17 and Period 3. Group 17 elements are known as halogens.

2. **Understand Valence Electrons**:
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