Write down important properties of ionic solids.

Explanation

### Step-by-Step Solution:

1. **High Melting and Boiling Points**:
- Ionic solids have high melting and boiling points due to the strong electrostatic forces of attraction between the positively charged ions (cations) and negatively charged ions (anions). This strong attraction requires a significant amount of energy to break, resulting in high melting and boiling points.

2. **Hard and Brittle**:
- Ionic solids are hard because of the strong ionic bonds that hold the ions in a rigid lattice structure. However, they are also brittle. When a force is applied, the layers of ions can shift, causing like charges to align and repel each other, leading to the breaking of the solid.

...