An example of covalent solid is:

Options

A. MgO
B. Mg
C. SiC
D. `CaF_(2)`

Explanation

To determine an example of a covalent solid from the given options, we need to analyze each option based on the type of bonding present in the solid.

### Step-by-Step Solution:

1. **Understanding Covalent Solids**:
- Covalent solids are characterized by atoms that are bonded together through strong covalent bonds. These bonds involve the sharing of electrons between atoms.

2. **Analyzing the Options**:
- **Option A: MgO (Magnesium Oxide)**:
- Magnesium (Mg) forms Mg²⁺ ions and oxygen (O) forms O²⁻ ions. The bonding in MgO is due to strong electrostatic forces between these oppositely charged ions, making it an ionic solid.

- **Option B: Mg (Magnesium)**:
- Magnesium is a metal, and in its solid state, it exhibits metallic bonding, where metal atoms are held together by a "sea of electrons." Therefore, it is a metallic solid, not a covalent solid.

- **Option C: SiC (Silicon Carbide)**:
- Silicon (Si) and carbon (C) are both nonmetals and they form a strong covalent bond by sharing electrons. This makes SiC a covalent solid.

- **Option D: CaF₂ (Calcium Fluoride)**:
- Calcium (Ca) forms Ca²⁺ ions and fluorine (F) forms F⁻ ions. The bonding in CaF₂ is also due to strong electrostatic forces between these ions, classifying it as an ionic solid.

3. **Conclusion**:
- From the analysis, the only option that represents a covalent solid is **SiC (Silicon Carbide)**.

### Final Answer:
The example of a covalent solid is **SiC (Silicon Carbide)**.

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