What type of compounds are purified by sublimation?

Explanation

**Step-by-Step Solution:**

1. **Understanding Sublimation**:
- Sublimation is the process where a solid changes directly into a gas without passing through the liquid state.
- For a substance to undergo sublimation, its vapor pressure must equal the atmospheric pressure at a temperature below its melting point.

2. **Conditions for Sublimation**:
- The vapor pressure of the substance must be significantly lower than its melting point. This ensures that when the solid is heated, it can transition directly to the gaseous state.
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