An element X belongs to group 17 and third period of the periodic table
Write electronic configuration of the element. What is its valency?

Explanation

To solve the question, we will follow these steps:

### Step 1: Identify the Element
The element X belongs to Group 17 and the third period of the periodic table. Group 17 elements are known as halogens. The halogens in the third period is chlorine (Cl).

### Step 2: Determine the Atomic Number
Chlorine has an atomic number of 17. This means it has 17 electrons.

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