Which of the following compounds is a good conductor of electricity in solution state?

Options

A. Covalent
B. Molecular
C. Metallic
D. Ionic

Explanation

To determine which compound is a good conductor of electricity in the solution state, we need to analyze the properties of different types of solids and their behavior in solution.

### Step-by-Step Solution:

1. **Identify the Types of Solids**: The question presents us with different types of solids, namely covalent solids, molecular solids, metallic solids, and ionic solids.

2. **Covalent Solids**:
- Covalent solids consist of atoms bonded together by covalent bonds.
- Example: Silicon forms a covalent solid.
- **Conductivity**: Covalent solids are generally poor conductors of electricity because they do not have free-moving charged particles. Therefore, they cannot conduct electricity in either solid or liquid states.
- **Conclusion**: Covalent solids are not good conductors of electricity.

3. **Molecular Solids**:
- Molecular solids are formed by molecules held together by intermolecular forces (like hydrogen bonding).
- Example: Ice (solid water).
- **Conductivity**: Like covalent solids, molecular solids are also poor conductors of electricity in both solid and liquid states because they lack free ions or electrons.
- **Conclusion**: Molecular solids are not good conductors of electricity.

4. **Metallic Solids**:
- Metallic solids consist of metal atoms that are bonded together and have a 'sea of electrons' that allows for conductivity.
- Example: Sodium (Na).
- **Conductivity**: Metallic solids are good conductors of electricity in solid form due to the mobility of electrons. However, the question specifically asks about the solution state.
- **Conclusion**: While metallic solids conduct electricity well, they do not dissociate into ions in solution.

5. **Ionic Solids**:
- Ionic solids are composed of ions held together by ionic bonds.
- Example: Sodium chloride (NaCl).
- **Conductivity**: In solid state, the ions are fixed in a crystal lattice and cannot move freely, hence they do not conduct electricity. However, when dissolved in water, the ionic bonds break, and the ions (Na+ and Cl-) become free to move. This mobility of ions allows ionic compounds to conduct electricity in solution.
- **Conclusion**: Ionic solids are good conductors of electricity in the solution state.

### Final Answer:
The compound that is a good conductor of electricity in the solution state is **ionic solids**.

---