Which of these is not a fossil fuel?

Options

A. Coal
B. biogas
C. natural gas
D. petroleum

Answer

To determine which of the given options is not a fossil fuel, we need to first understand what fossil fuels are and then analyze each option provided.

### Step-by-Step Solution:

1. **Define Fossil Fuels**:
Fossil fuels are natural substances formed from the remains of dead plants and animals that have been buried under layers of earth for millions of years. They include coal, oil (petroleum), and natural gas.

2. **Analyze Each Option**:
- **Option A: Coal**: Coal is a fossil fuel formed from the remains of ancient plants that were subjected to heat and pressure over millions of years. Therefore, coal is a fossil fuel.

- **Option B: Biogas**: Biogas is produced from the decomposition of organic matter by microorganisms in the absence of oxygen. It is not formed from ancient remains buried for millions of years, so biogas is not considered a fossil fuel.

- **Option C: Natural Gas**: Natural gas is a fossil fuel that is often found alongside oil and is formed from the remains of marine organisms. Thus, natural gas is a fossil fuel.

- **Option D: Petroleum**: Petroleum (or crude oil) is also a fossil fuel formed from the remains of ancient marine organisms buried under layers of sediment. Therefore, petroleum is a fossil fuel.

3. **Conclusion**:
From the analysis, we see that the only option that is not a fossil fuel is **Biogas (Option B)**.

### Final Answer:
The answer is **B: Biogas**.