Which of the following is correct about a constituent of biogas?

Options

A. 30% - 40% methane
B. 50% - 70% `CO_2`
C. `50%- 70%` methane
D. `20%` methane

Answer

To determine the correct statement about the constituents of biogas, we need to analyze the composition of biogas. Here’s a step-by-step solution:

### Step 1: Understand the Composition of Biogas
Biogas is primarily composed of two main gases: methane (CH₄) and carbon dioxide (CO₂).

### Step 2: Identify the Proportions of Methane and Carbon Dioxide
- Methane typically constitutes about 50% to 75% of biogas.
- Carbon dioxide makes up about 25% to 50% of biogas.

### Step 3: Consider Trace Gases
In addition to methane and carbon dioxide, biogas contains trace amounts of other gases, including:
- Nitrogen (0% to 10%)
- Hydrogen (0% to 1%)
- Hydrogen sulfide (0.1% to 0.5%)
- Oxygen (0% to 0.5%)

### Step 4: Evaluate the Options
Now, we need to evaluate the options provided in the question:
1. If an option states that biogas contains 30% to 40% methane, this is incorrect based on our understanding.
2. If an option states that biogas contains 50% to 70% methane, this is partially correct, as it falls within the acceptable range.
3. If an option states that biogas contains 50% to 75% methane, this is also correct as it aligns with the known composition of biogas.
4. If an option states that biogas contains 20% methane, this is incorrect.

### Step 5: Conclusion
Based on the analysis, the correct option regarding the constituents of biogas is the one that states it contains 50% to 75% methane.