It is mainly found in 'Bio-Gas' -

Options

A. Chlorine
B. Hydrogen
C. Ethylene
D. Methane

Explanation

### Step-by-Step Solution:

1. **Understanding Biogas**:
- Biogas is a type of renewable energy produced from the decomposition of organic matter (biomass) in the absence of oxygen, a process known as anaerobic digestion.

2. **Composition of Biogas**:
- The primary components of biogas are methane (CH₄) and carbon dioxide (CO₂). Methane is the main component, making up a significant portion of the gas.

3. **Identifying the Options**:
- The question asks for the main component found in biogas. The options provided are chlorine, hydrogen, ethylene, and methane.

4. **Analyzing the Options**:
- Chlorine: A chemical element, not found in biogas.
- Hydrogen: While it can be present in small amounts, it is not the main component.
- Ethylene: A hydrocarbon, but not a primary component of biogas.
- Methane: This is the primary component of biogas.

5. **Conclusion**:
- Based on the analysis, the correct answer is **methane (CH₄)**, as it is the main component of biogas.

### Final Answer:
- Methane (CH₄) is mainly found in biogas.

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