Biogas , produced by fermentation of manure, sewage cattle dung etc. predominantly comprieses :

Options

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

Explanation

**Step-by-Step Solution:**

1. **Understanding Biogas**: Biogas is a mixture of gases produced by the anaerobic digestion of organic matter, such as manure, sewage, and cattle dung. It is primarily used as a renewable energy source.

2. **Components of Biogas**: The primary gases found in biogas are methane (CH₄) and carbon dioxide (CO₂). Other gases may also be present in smaller amounts, such as hydrogen sulfide (H₂S) and water vapor (H₂O).

3. **Role of Microbes**: The fermentation process involves specific microorganisms, particularly methanogens, which are responsible for the production of methane. These microbes break down organic material in the absence of oxygen.

4. **Evaluating the Options**:
- **Option A**: Methane, Nitrogen, and Hydrogen - Nitrogen is not a significant component of biogas.
- **Option B**: Methane and Carbon Dioxide - This is a correct representation of the predominant components of biogas.
- **Option C**: Methane and Carbon Monoxide - Carbon monoxide is not a typical component of biogas.
- **Option D**: Methane and Nitric Oxide - Nitric oxide is also not a part of biogas.

5. **Conclusion**: Based on the evaluation of the options, the predominant gases in biogas produced from fermentation of manure and sewage are methane and carbon dioxide. Therefore, the correct answer is **Option B: Methane and Carbon Dioxide**.

---