Why is biogas considered an excellent fuel?

Explanation

### Step-by-Step Solution:

1. **Definition of Biogas**: Biogas is a renewable energy source produced from the breakdown of organic matter in the absence of oxygen (anaerobic digestion).

2. **Composition of Biogas**: The primary component of biogas is methane (50-70%), which is a highly combustible gas. It also contains carbon dioxide (25-45%) and trace amounts of other gases.

3. **Formation Process**: Biogas is formed through the anaerobic decay of organic materials such as manure and plant residues. This process involves bacteria that break down the organic matter without oxygen, resulting in the production of gases.

...