Anaerobic bacteria digest animal waste and produce biogas (Change - A).
The biogas is then burnt as fuel (Change - B). The following statements pertain to these changes. Choose the correct one.

Options

A. Process - A is a chemical change.
B. Process - B is a chemical change.
C. Both processes A and B are chemical changes.
D. None of these processes is a chemical change.

Answer

To solve the question regarding the changes A and B related to anaerobic bacteria and biogas, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding Change A:**
- In Change A, anaerobic bacteria digest animal waste to produce biogas.
- This process involves a chemical reaction where the bacteria break down the organic matter in the animal waste.
- As a result, new substances (biogas) are formed from the initial material (animal waste).

**Hint:** Identify whether new substances are formed during a process to determine if it is a chemical change.

2. **Identifying Change A as a Chemical Change:**
- Since new substances (biogas) are produced from the digestion of animal waste, Change A is classified as a chemical change.
- The properties of biogas are different from those of animal waste, confirming that a chemical change has occurred.

**Hint:** Remember that in a chemical change, the original substances cannot be easily reverted back to their initial forms.

3. **Understanding Change B:**
- In Change B, the biogas is burnt as fuel.
- Burning biogas involves a combustion reaction, which also results in the formation of new substances, primarily carbon dioxide (CO2) and possibly water vapor.

**Hint:** Look for processes that involve burning or reacting substances to identify chemical changes.

4. **Identifying Change B as a Chemical Change:**
- Since burning biogas produces new substances (like CO2), Change B is also classified as a chemical change.
- The properties of the products (CO2 and water vapor) are different from those of the biogas.

**Hint:** Consider the end products of a reaction to determine if a chemical change has occurred.

5. **Conclusion:**
- Both Change A (digestion of animal waste to produce biogas) and Change B (burning biogas) are chemical changes.
- Therefore, the correct statement is that both processes A and B are chemical changes.

**Hint:** Summarize your findings to confirm the classification of each change.

### Final Answer:
Both Change A and Change B are chemical changes.