Elements belonging to different groups of the periodic table are given below. If the element X forms a chloride whose formula is '`XCl_2`' then element 'X' belongs to the group whose representative element is:

Options

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

Explanation

To determine which group element X belongs to based on the formula of its chloride, XCl₂, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Formula**:
The formula XCl₂ indicates that for every one atom of element X, there are two atoms of chlorine (Cl). This suggests that the valency of chlorine is 1 (since it needs one electron to complete its octet) and the valency of element X must be 2 (to balance the two chlorine atoms).

**Hint**: Remember that the subscript in a chemical formula indicates how many atoms of each element are present.

2. **Identifying the Valency of Chlorine**:
Chlorine (Cl) has an atomic number of 17, with an electronic configuration of 2, 8, 7. To achieve a stable octet, chlorine needs to gain 1 electron, giving it a valency of 1.

**Hint**: Check the electronic configuration of elements to determine how many electrons they need to gain or lose to achieve a stable octet.

3. **Determining the Valency of Element X**:
Since the formula is XCl₂, and we have established that the valency of chlorine is 1, the valency of element X must be 2 (because 2 chlorine atoms are needed to balance the charge).

**Hint**: The valency of an element can often be inferred from the number of atoms of other elements it combines with in a compound.

4. **Identifying Possible Elements**:
Now we need to identify which elements from the periodic table have a valency of 2. Common elements with a valency of 2 include Magnesium (Mg), Calcium (Ca), and Barium (Ba).

**Hint**: Look at the periodic table and identify the groups. Elements in Group 2 typically have a valency of 2.

5. **Conclusion**:
Among the elements listed, Magnesium (Mg) is a representative element of Group 2 that forms a chloride with the formula MgCl₂, which matches our derived formula of XCl₂. Therefore, element X belongs to the group whose representative element is Magnesium (Mg).

**Final Answer**: Element X belongs to the group whose representative element is Magnesium (Mg).