Methanogens have a unique form of energy metabolism in which ............. is used to reduce ……. to …….

Explanation

**Step-by-Step Solution:**

1. **Identify the Organism**: Methanogens are a group of microorganisms that are primarily known for their ability to produce methane. They are a type of archaea.

2. **Understanding Energy Metabolism**: Methanogens have a unique form of energy metabolism. This means they have a specific way of obtaining energy that is different from other organisms.

3. **Identify the Reactants and Products**: In the process of energy metabolism, methanogens utilize hydrogen (H2) as a key reactant.

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