Heating of methane in the absence of air is called.

Options

A. combustion
B. decarbonxylation
C. pyrolysis
D. photolysis

Explanation

To solve the question "Heating of methane in the absence of air is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Process**:
- When methane (CH₄) is heated without the presence of air (oxygen), it undergoes a chemical process.

2. **Identifying the Type of Reaction**:
- The process of heating a substance in the absence of air is known as pyrolysis. Pyrolysis involves the thermal decomposition of materials at elevated temperatures in an inert atmosphere.

3. **Chemical Reaction**:
- During pyrolysis of methane, it can break down into simpler substances. The reaction can produce hydrogen gas (H₂) and carbon (C) as products.
- The simplified reaction can be represented as:
\[ CH₄ \rightarrow C + 2H₂ \]

4. **Reversibility of the Reaction**:
- This reaction can be reversible, meaning that the products can potentially react to form the original reactant under certain conditions.

5. **Conclusion**:
- Therefore, the process of heating methane in the absence of air is called pyrolysis.

### Final Answer:
The correct answer is **pyrolysis**.

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