Can the following change be reversed?
Making biogas from cow dung

Explanation

**Step-by-Step Solution:**

1. **Understanding the Process**: The question asks whether the change of making biogas from cow dung can be reversed. To answer this, we first need to understand what happens during the process of making biogas.

2. **Chemical Change**: The process of making biogas involves a chemical change. Cow dung is broken down by bacteria, specifically Methanogen bacteria, which convert the organic matter in cow dung into biogas, primarily methane.

3. **Irreversibility of Chemical Changes**: In a chemical change, the original substances (in this case, cow dung) are transformed into new substances (biogas). Once this transformation occurs, it is usually not possible to revert the new substances back to the original substances.

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