If element X forms a chloride with the formula `XCl_3`, then X would most likely belong to the same group of the Modern Periodic Table as :

Options

A. Na
B. Br
C. Al
D. Mg

Explanation

To determine which group element X belongs to based on the formula of its chloride, XCl₃, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Compound**: The formula XCl₃ indicates that element X forms a compound with chlorine (Cl) in a 1:3 ratio. This means that one atom of X combines with three atoms of chlorine.

2. **Determining the Charge of X**: Since chlorine typically has a charge of -1 (as it gains one electron to achieve a stable electronic configuration), and there are three chlorine atoms, the total negative charge contributed by chlorine is -3. Therefore, for the compound to be neutral, element X must have a charge of +3.

3. **Identifying the Group**: Elements that form +3 ions typically belong to group 13 of the periodic table. This group includes elements like aluminum (Al), gallium (Ga), and indium (In).

4. **Finding the Element with +3 Charge**: We need to identify an element that can lose three electrons to achieve a +3 charge. The electronic configuration of aluminum (atomic number 13) is 1s² 2s² 2p⁶ 3s² 3p¹. Aluminum has three electrons in its outermost shell (3s² 3p¹), which it can lose to form Al³⁺.

5. **Conclusion**: Therefore, element X, which forms XCl₃, most likely belongs to group 13 of the Modern Periodic Table, with aluminum being a prime example.

### Final Answer:
Element X would most likely belong to the same group of the Modern Periodic Table as aluminum (Al), which is group 13.

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