Which of the following is a covalent solid ?

Options

A. `CO_(2)(s)`
B. `H_(2)O(s)`
C. Diamond
D. NaCl(s)

Answer

To determine which of the following is a covalent solid, we need to analyze the types of solids listed:

1. **CO2 (Carbon Dioxide)**: This is a molecular solid. It consists of discrete molecules held together by van der Waals forces. Therefore, it is not a covalent solid.

2. **H2O (Water)**: Similar to CO2, water is also a molecular solid. It consists of molecules held together by hydrogen bonds and van der Waals forces. Thus, it is not a covalent solid.

3. **Diamond**: Diamond is a well-known example of a covalent solid. In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral structure, forming a three-dimensional network. This makes diamond a covalent solid.

4. **NaCl (Sodium Chloride)**: NaCl is an ionic solid. It consists of positively charged sodium ions and negatively charged chloride ions held together by ionic bonds. Therefore, it is not a covalent solid.

5. **Ionic Solid**: This is a general term that refers to solids made up of ions held together by ionic bonds. As mentioned, NaCl is an example of an ionic solid.

Based on this analysis, the only covalent solid among the options provided is **Diamond**.

### Final Answer:
**Diamond** is a covalent solid.