According to Oparin, which one of the following was not present in the primitive atmospehre of the earth?

Options

A. Methane
B. Oxygen
C. Hydrogen
D. Water vapour

Explanation

**Step-by-Step Solution:**

1. **Understand the Context**: The question asks about the constituents of the primitive atmosphere of the Earth according to the theory proposed by Oparin. This theory is related to the origin of life and is known as chemical evolution.

2. **Identify Key Scientists**: Recognize that Oparin, along with Haldane, contributed significantly to the understanding of the early Earth’s atmosphere and the conditions that may have led to the formation of life.

3. **Characteristics of Primitive Atmosphere**: According to Oparin, the primitive atmosphere was highly reducing, meaning it lacked free oxygen (O2). Instead, it primarily consisted of gases such as methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor (H2O).

4. **List the Possible Options**: The question likely provides multiple-choice options. Identify which of these options represent gases that were present in the primitive atmosphere and which one does not.

5. **Determine the Correct Answer**: Since the primitive atmosphere, as described by Oparin, did not contain free oxygen, the correct answer to the question is the option that indicates the presence of oxygen.

6. **Final Conclusion**: Therefore, according to Oparin's theory of chemical evolution, the constituent that was not present in the primitive atmosphere of the Earth is oxygen (O2).

**Answer**: Oxygen (O2) was not present in the primitive atmosphere of the Earth according to Oparin.

---