Which of the following was not found in free form during origin of life:

Options

A. Ammonia
B. Methane
C. Oxygen
D. Hydrogen

Answer

### Step-by-Step Solution:

1. **Understanding the Context**: The question asks which of the given substances was not found in free form during the origin of life on Earth. The options provided are Ammonia, Methane, Oxygen, and Hydrogen.

2. **Analyzing the Primitive Atmosphere**: During the early stages of Earth's atmosphere, it was primarily composed of water vapor, carbon monoxide, carbon dioxide, and hydrogen. This indicates that hydrogen was abundant.

3. **Identifying Greenhouse Gases**: The primitive atmosphere also contained greenhouse gases such as carbon dioxide (CO2) and methane (CH4). These gases contributed to a high temperature on early Earth due to their ability to absorb infrared radiation.

4. **Role of Energy Sources**: The high temperatures, along with ultraviolet (UV) light and lightning, facilitated chemical reactions among the atmospheric components. This environment was conducive to the formation of various compounds.

5. **Formation of Compounds**: In this reducing atmosphere, hydrogen combined with other elements to form compounds like water (H2O), ammonia (NH3), methane (CH4), and cyanide (HCN).

6. **Oxygen's State**: Oxygen, however, was not found in a free state during this time. Instead, it was primarily combined with other elements to form oxides (e.g., iron oxides, silicon oxides). This indicates that oxygen was not available as a free gas in the atmosphere.

7. **Conclusion**: Based on the analysis, the substance that was not found in free form during the origin of life is **Oxygen**.

### Final Answer:
**Oxygen** was not found in free form during the origin of life.

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