Which of the following will be most covalent :-

Options

A. `NaCl`
B. `Na_(2)S`
C. `MgCl_(2)`
D. `MgS`

Answer

To determine which of the given compounds is the most covalent, we will analyze the options based on the principles of covalent character in ionic compounds.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are NaCl, Na2S, MgCl2, and MgS.

2. **Understand Covalent Character**: Covalent character in ionic compounds is influenced by the size of the ions and their charge. Smaller ions with higher charges tend to have a greater covalent character due to their ability to polarize the electron cloud of the opposing ion.

3. **Analyze the Cations**:
- **Na+**: Sodium ion is larger and has a +1 charge.
- **Mg2+**: Magnesium ion is smaller and has a +2 charge.

4. **Analyze the Anions**:
- **Cl-**: Chloride ion is larger and has a -1 charge.
- **S2-**: Sulfide ion is larger and has a -2 charge.

5. **Comparing the Compounds**:
- **NaCl**: Na+ and Cl- have a lower charge and larger size, leading to less covalent character.
- **Na2S**: Na+ is still +1, but S2- has a higher charge, which increases covalent character slightly.
- **MgCl2**: Mg2+ has a higher charge than Na+, which increases covalent character compared to NaCl.
- **MgS**: Mg2+ and S2- both have higher charges, leading to significant polarization and thus a higher covalent character.

6. **Conclusion**: Among the given compounds, MgS has the most covalent character due to the small size and high charge of Mg2+ and S2- ions.

### Final Answer:
**MgS is the most covalent compound among the options given.**

---