An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
Where in the periodic table are elements X and Y placed?

Explanation

To determine where elements X and Y are placed in the periodic table based on their atomic numbers, we can follow these steps:

### Step 1: Identify Element X
- The atomic number of element X is 17.
- In the periodic table, the element with atomic number 17 is Chlorine (Cl).

### Step 2: Identify Element Y
- The atomic number of element Y is 20.
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