With reference of first three periods of the periodic table.
Valency of elements in group 17

Explanation

To determine the valency of elements in Group 17 of the first three periods of the periodic table, we will follow these steps:

### Step 1: Identify the Elements in Group 17
Group 17 of the periodic table is known as the halogens. In the first three periods, the elements present in this group are:
- Period 1: No element
- Period 2: Fluorine (F)
- Period 3: Chlorine (Cl)

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