Under what conditions do we use fractional distillation ?

Explanation

### Step-by-Step Solution:

1. **Definition of Fractional Distillation**: Fractional distillation is a technique used to separate components of a mixture based on differences in their boiling points. It is particularly useful for separating miscible liquids.

2. **Conditions for Use**:
- **Miscible Mixtures**: Fractional distillation is applied when dealing with miscible liquids, which are liquids that can mix in any proportion without separating into two phases.
- **Boiling Point Difference**: The key condition for using fractional distillation is that the boiling points of the components in the mixture must differ by less than 25 degrees Celsius. This small difference makes it challenging to separate the components using simple distillation.

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