An element X (atomic number 12) reacts with another element Y (atomic number 17 ) to form a Compound Z. Which of the following statements are true regarding this compound ?
I. Molecular formula of Z is `XY_(2)`
(II) It is soluble in water.
(III) X and Y are joined by sharing of electrons.
(IV) It would conduct electricity in the molten state.

Options

A. II and III
B. I and II
C. I, III and IV
D. I, II and IV

Explanation

To solve the question, we need to analyze the properties of the compound formed by elements X and Y, where X has an atomic number of 12 and Y has an atomic number of 17.

### Step-by-Step Solution:

1. **Identify the Elements**:
- The element X with atomic number 12 is Magnesium (Mg).
- The element Y with atomic number 17 is Chlorine (Cl).

2. **Determine the Valencies**:
- Magnesium (Mg) has a valency of +2 (it tends to lose 2 electrons).
- Chlorine (Cl) has a valency of -1 (it tends to gain 1 electron).

3. **Formulate the Compound**:
- To balance the charges, we need 2 Chlorine atoms for every Magnesium atom. Therefore, the formula for the compound Z is MgCl₂, which can be represented as XY₂.

4. **Evaluate the Statements**:
- **Statement I**: The molecular formula of Z is XY₂.
- This statement is **True** because the formula is indeed MgCl₂ or XY₂.

- **Statement II**: It is soluble in water.
- This statement is **True**. Ionic compounds like MgCl₂ are soluble in water due to the polar nature of both the compound and water, allowing them to interact and dissolve.

- **Statement III**: X and Y are joined by sharing of electrons.
- This statement is **False**. The bond between Mg and Cl is ionic, not covalent. In ionic bonds, electrons are transferred, not shared.

- **Statement IV**: It would conduct electricity in the molten state.
- This statement is **True**. Ionic compounds conduct electricity when molten or dissolved in water because they dissociate into ions that are free to move.

5. **Conclusion**:
- The true statements regarding the compound Z are: I, II, and IV.

### Summary of True Statements:
- I. True
- II. True
- III. False
- IV. True