A particular solid is very hard and has a very high melting point.In solid state it is nonconductor and its melt is a conductor of electricity. Classify the solid.

Options

A. metallic
B. molecular
C. network
D. ionic

Explanation

To classify the solid based on the given properties, we can follow these steps:

### Step 1: Analyze the Properties of the Solid
The solid is described as:
- Very hard
- Very high melting point
- Non-conductor in solid state
- Conductor of electricity in molten state

### Step 2: Consider the Types of Solids
The main types of solids are:
1. Metallic solids
2. Molecular solids
3. Network solids
4. Ionic solids

### Step 3: Evaluate Each Type of Solid
- **Metallic Solids**: Generally good conductors of electricity in both solid and molten states, not fitting the non-conductor property in solid state.
- **Molecular Solids**: Typically have low melting points and are soft, which does not match the high hardness and melting point.
- **Network Solids**: Very hard and have high melting points, but they do not conduct electricity in either state.
- **Ionic Solids**: Known for being very hard and having high melting points due to strong ionic bonds. They do not conduct electricity in solid state because the ions are fixed in place, but they conduct electricity when melted because the ions are free to move.

### Step 4: Conclusion
Based on the analysis, the solid described in the question matches the characteristics of **ionic solids**. Therefore, the classification of the solid is:

**Answer: Ionic Solid (Option 4)**

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