An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
Classify X and Y as metal (s), non-metal (s) or metalloid (s).

Explanation

To classify the elements X and Y based on their atomic numbers and properties, we can follow these steps:

### Step 1: Identify the Elements
- Element X has an atomic number of 17. Referring to the periodic table, the element with atomic number 17 is Chlorine (Cl).
- Element Y has an atomic number of 20. The element with atomic number 20 is Calcium (Ca).

### Step 2: Classify Element X (Chlorine)
- Chlorine (Cl) is located in Group 17 of the periodic table, which is known as the halogens. Halogens are non-metals.
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