What is meant by carbonization ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Carbonization**: Carbonization is a process that involves the transformation of organic materials into carbon-rich substances.

2. **Heating of Coal**: In carbonization, coal is subjected to high temperatures. This heating occurs in the absence of air (or oxygen).

3. **Absence of Air**: The absence of air is crucial because it prevents combustion. If air were present, the coal would burn instead of undergoing carbonization.

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