Which of the following compound is covalent?

Options

A. `SiO_(2)`
B. `S_(8)`
C. `CaC_(2)`
D. `Na_(2)S`

Explanation

To determine which of the following compounds is covalent, we need to analyze the nature of the bonds in each compound based on the difference in electronegativity between the atoms involved.

### Step-by-Step Solution:

1. **Understanding Covalent and Ionic Bonds**:
- Covalent bonds typically form between non-metals with similar electronegativities, resulting in a low difference in electronegativity.
- Ionic bonds form between metals and non-metals with a high difference in electronegativity.

2. **Analyzing the Compounds**:
- **Na2S** (Sodium Sulfide):
- Sodium (Na) is a metal and sulfur (S) is a non-metal.
- The electronegativity difference between Na and S is high, indicating that Na2S is predominantly ionic.

- **Calcium Carbide (CaC2)**:
- Calcium (Ca) is a metal and carbon (C) is a non-metal.
- The electronegativity difference between Ca and C is also high, suggesting that CaC2 is predominantly ionic.

- **S8 (Sulfur)**:
- S8 consists of sulfur atoms bonded to each other.
- Since both atoms are non-metals, the electronegativity difference is negligible, indicating that S8 has covalent bonds.

- **SiO2 (Silicon Dioxide)**:
- Silicon (Si) and oxygen (O) are both non-metals.
- The electronegativity difference between Si and O is low, suggesting that SiO2 is predominantly covalent.

3. **Conclusion**:
- From the analysis, we find that:
- Na2S is ionic.
- CaC2 is ionic.
- S8 is covalent.
- SiO2 is covalent.
- Therefore, the compounds that are covalent are **S8 and SiO2**.

### Final Answer:
The covalent compounds among the options are **S8 and SiO2**.