Which of the following is covalent ?

Options

A. NaCl
B. KCl
C. `BeCl_(2)`
D. `HgCl_(2)`

Explanation

To determine which of the given compounds is covalent, we will analyze the nature of each compound based on the types of ions involved and their characteristics.

### Step 1: Identify the Compounds
The compounds given are:
- A: NaCl (Sodium Chloride)
- B: KCl (Potassium Chloride)
- C: BeCl₂ (Beryllium Chloride)
- D: HgCl₂ (Mercury Chloride)

### Step 2: Understand Ionic vs Covalent Bonds
Ionic bonds typically form between metals and nonmetals, where electrons are transferred from the metal to the nonmetal. Covalent bonds, on the other hand, involve the sharing of electrons between atoms.

### Step 3: Analyze Each Compound
1. **NaCl (Sodium Chloride)**: Sodium (Na) is a metal and chlorine (Cl) is a nonmetal. NaCl is primarily ionic due to the large difference in electronegativity between Na and Cl.

2. **KCl (Potassium Chloride)**: Similar to NaCl, potassium (K) is also a metal and chlorine (Cl) is a nonmetal. KCl is also primarily ionic.

3. **BeCl₂ (Beryllium Chloride)**: Beryllium (Be) is a metal, but it has a small ionic radius and a relatively high charge density. This allows it to polarize the electron cloud of the chloride ions, leading to a significant covalent character. Thus, BeCl₂ exhibits covalent characteristics.

4. **HgCl₂ (Mercury Chloride)**: Mercury (Hg) can exhibit both ionic and covalent characteristics. However, HgCl₂ is often considered to have more covalent character due to the nature of mercury's bonding.

### Step 4: Compare Covalent Character
According to Fajans' rules, the covalent character of a compound increases with:
- Smaller cation size
- Higher charge on the cation
- Larger anion size

In this case, Be²⁺ has a small size and a high charge, which increases its covalent character. Therefore, BeCl₂ is more covalent than NaCl and KCl.

### Conclusion
The compound that exhibits covalent character among the given options is **C: BeCl₂ (Beryllium Chloride)**.

---