Biogas produced by the fermentation of manure , sewage , cattle dung , etc., predominantly comprises

Options

A. Methane,nitrogen ,and hydrogen
B. Methane and carbon dioxide
C. Methane and carbon monoxide
D. Methane and nitric oxide

Answer

### Step-by-Step Solution:

1. **Understanding Biogas**: Biogas is a type of gaseous fuel that is produced through the fermentation of organic materials such as manure, sewage, and cattle dung.

2. **Fermentation Process**: The production of biogas occurs through fermentation, which is a biochemical process. This process requires the breakdown of organic matter in the absence of oxygen (anaerobic conditions).

3. **Role of Methanogens**: The fermentation process is facilitated by specific microorganisms known as methanogens. These bacteria thrive in anaerobic environments and are responsible for converting organic matter into methane.

4. **Main Components of Biogas**: The primary component of biogas is methane (CH4). Along with methane, carbon dioxide (CO2) is also a significant component of biogas.

5. **Exclusion of Other Gases**: The question provides several options, including nitrogen, hydrogen, carbon monoxide, and nitric oxide. However, these gases are not predominant in biogas. The main constituents are methane and carbon dioxide.

6. **Conclusion**: Based on the above points, the correct answer to the question is that biogas predominantly comprises methane and carbon dioxide, which corresponds to option B.

### Final Answer:
**Biogas produced by the fermentation of manure, sewage, cattle dung, etc., predominantly comprises methane and carbon dioxide. (Option B)**

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