Which point defect lowers the density of a crystal?

Explanation

### Step-by-Step Solution:

1. **Understanding Point Defects**:
- Point defects are imperfections in the crystal lattice that occur at a single point. They can affect the properties of the crystal, including its density.

2. **Identifying Types of Point Defects**:
- The common types of point defects include:
- **Vacancy Defects**: Missing atoms in the lattice.
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