Solid `A` is a very hard electrical insulator in solid as well as in molten state and melts at extermely high temperature. What type of solid is it?

Options

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

Explanation

To solve the question about solid A, we need to analyze the properties given:

1. **Very Hard**: This indicates that the solid has a strong structure, likely due to strong bonding.
2. **Electrical Insulator in Solid and Molten State**: This suggests that the solid does not conduct electricity, which is a key characteristic of certain types of solids.
3. **Melts at Extremely High Temperature**: This implies that the bonds holding the solid together are very strong, requiring a lot of energy to break.

Now, let's evaluate the types of solids based on these properties:

### Step 1: Identify the Types of Solids
- **Ionic Solids**: These are typically good conductors of electricity when molten or dissolved in water, so they do not fit the criteria of being an insulator in both states.
- **Metallic Solids**: These are also good conductors of electricity due to the presence of free-moving electrons, thus they do not fit as well.
- **Molecular Solids**: These tend to be poor conductors, but they do not exhibit the extreme hardness or high melting points described in the question.
- **Covalent (Network) Solids**: These solids are characterized by a network of covalent bonds, making them very hard and typically insulators in both solid and molten states. They also have very high melting points.

### Step 2: Conclusion
Given the properties of solid A, it is most consistent with being a **covalent solid**. Examples include silicon dioxide (SiO2) and diamond, both of which are hard, insulative, and have high melting points.

### Final Answer
Solid A is a **covalent solid**.

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