Marsh gas is ……………………

Explanation

**Step-by-Step Solution:**

1. **Identify Marsh Gas**: The question asks about Marsh gas. The first step is to recognize that Marsh gas is commonly known as methane.

2. **Production Process**: Marsh gas (methane) is produced through a specific biological process. It is formed by the anaerobic decomposition of organic matter.

3. **Source of Organic Matter**: The organic matter from which Marsh gas is produced primarily includes vegetable matter and the contents found in the rumen of herbivorous animals.

4. **Environmental Conditions**: This decomposition process occurs in anaerobic conditions, meaning it takes place without the presence of oxygen. This is often found in underwater environments or marshy areas.

5. **Final Definition**: Therefore, Marsh gas can be defined as methane, which is produced by the anaerobic bacterial decomposition of vegetable matter and the rumen of herbivorous animals, typically in underwater or marshy conditions.

**Final Answer**: Marsh gas is also known as methane, produced by anaerobic bacterial decomposition of vegetable matter and the rumen of herbivorous animals under water.

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