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

Answer

To determine the type of solid described in the question, we will analyze the properties given for solid A step by step.

### Step 1: Identify the Properties of Solid A
The question states that solid A is:
- Very hard
- An electrical insulator in both solid and molten states
- Melts at extremely high temperatures

### Step 2: Classify the Type of Solid
Based on the properties identified:
- **Very Hard**: This suggests that the solid has a strong bonding structure.
- **Electrical Insulator**: This indicates that the solid does not have free-moving charged particles (like electrons) that can conduct electricity.
- **High Melting Point**: This implies that a significant amount of energy is required to break the bonds holding the solid together.

### Step 3: Consider the Types of Solids
There are several types of solids:
1. **Metallic Solids**: Generally good conductors of electricity and have variable hardness.
2. **Ionic Solids**: Usually have high melting points and can conduct electricity when molten but are not insulators in solid form.
3. **Molecular Solids**: Typically soft and have lower melting points.
4. **Covalent Network Solids**: These are very hard, have high melting points, and are electrical insulators.

### Step 4: Conclusion
Given the properties of solid A, it is most consistent with a **covalent network solid**. An example of such a solid is diamond, which is very hard, an electrical insulator, and has an extremely high melting point.

### Final Answer
Solid A is a **covalent network solid** (e.g., diamond).

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