Which of these is a covalent solid?

Options

A. `Fe_(2)O_(3)`
B. Diamond
C. Graphite
D. All of these

Answer

To determine which of the given options is a covalent solid, we will analyze each option based on the characteristics of covalent solids.

### Step-by-Step Solution:

1. **Understanding Covalent Solids**:
- Covalent solids, also known as network solids, are materials where atoms are bonded together by covalent bonds in a continuous network. This results in a structure that can be viewed as a single giant molecule. The bonds are strong and localized, leading to high melting points and hardness.

2. **Analyzing the Options**:
- **Option 1: Fe2O3 (Iron(III) oxide)**:
- This compound is formed from iron (a metal) and oxygen (a non-metal). The bonding here is primarily ionic due to the significant difference in electronegativity between iron and oxygen. Therefore, Fe2O3 is not a covalent solid.

- **Option 2: Diamond**:
- Diamond is a form of carbon where each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This structure is what gives diamond its exceptional hardness and high melting point. Thus, diamond is a covalent solid.

- **Option 3: Graphite**:
- Graphite is another form of carbon where each carbon atom is bonded to three others in a planar hexagonal arrangement, with delocalized electrons between the layers. Despite the presence of layers, the covalent bonds within each layer make graphite a covalent solid.

- **Option 4: All of these**:
- Since we have established that Fe2O3 is not a covalent solid, this option cannot be correct.

3. **Conclusion**:
- The covalent solids among the options provided are diamond (Option 2) and graphite (Option 3). Therefore, the correct answer to the question "Which of these is a covalent solid?" is that both diamond and graphite are covalent solids.

### Final Answer:
- The covalent solids in the options provided are **diamond (Option 2)** and **graphite (Option 3)**.