Which of the following gas was not used by Miller is his experinent ?

Options

A. `CH_4`
B. `NH_3`
C. `H_2`
D. `O_2`

Explanation

**Step-by-Step Solution:**

1. **Understanding Miller's Experiment**:
- Miller conducted an experiment to simulate the conditions of primitive Earth to understand how organic compounds could form from inorganic gases.

2. **Identifying the Gases Used**:
- In his experiment, Miller used several inorganic gases that were believed to be present in the atmosphere of early Earth. These gases included:
- Methane (CH4)
- Ammonia (NH3)
- Hydrogen (H2)
- Water vapor (H2O)

3. **Recognizing the Absence of Oxygen**:
- It is important to note that oxygen (O2) was not included in Miller's experiment. The primitive Earth is thought to have had a reducing atmosphere, meaning it lacked free oxygen.

4. **Conclusion**:
- Therefore, the gas that was not used by Miller in his experiment is oxygen.

**Final Answer**: Oxygen (O2) was not used by Miller in his experiment.

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