Which substance will conduct the current in the solid state?

Options

A. Diamond
B. Graphite
C. Iodine
D. Sodium chloride

Answer

To determine which substance will conduct electricity in the solid state, we need to analyze the properties of each given substance: diamond, graphite, iodine, and sodium chloride.

### Step-by-Step Solution:

1. **Analyze Diamond (A)**:
- Diamond is a form of carbon where each carbon atom is tetrahedrally bonded to four other carbon atoms, forming a rigid three-dimensional structure.
- In this structure, there are no free electrons available to conduct electricity.
- **Conclusion**: Diamond does not conduct electricity in solid state.

2. **Analyze Graphite (B)**:
- Graphite is another form of carbon, but it has a layered structure. Each carbon atom is bonded to three other carbon atoms in a plane, forming hexagonal sheets.
- Within these layers, one electron from each carbon atom is delocalized, meaning it is free to move between the layers.
- This delocalization of electrons allows graphite to conduct electricity even in the solid state.
- **Conclusion**: Graphite conducts electricity in solid state.

3. **Analyze Iodine (C)**:
- Iodine consists of diatomic molecules (I2) held together by covalent bonds. In its solid state, these molecules form a crystalline structure.
- There are no free electrons available for conduction, as the covalent bonds do not break to release electrons.
- **Conclusion**: Iodine does not conduct electricity in solid state.

4. **Analyze Sodium Chloride (D)**:
- Sodium chloride (NaCl) forms an ionic lattice structure in solid state, where sodium ions (Na+) and chloride ions (Cl-) are held together by strong ionic bonds.
- In solid state, the ions are fixed in place and cannot move freely, which means there are no charge carriers available to conduct electricity.
- Sodium chloride only conducts electricity when it is dissolved in water or melted, allowing the ions to move freely.
- **Conclusion**: Sodium chloride does not conduct electricity in solid state.

### Final Answer:
Among the given substances, **only graphite (B)** conducts electricity in the solid state.

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