Find incorrect about the experiment of Van Niel:

Options

A. Experimental organisms were purple sulphur and green sulphur bacteria
B. Sulphur compound is used by bacteria as source of `H^(+)` and `e^(–)`
C. In photosynthesis, `CO_(2)` splits to produce free `O_(2)`
D. He used `CO_(2)` and `H_(2)S` as substrates

Answer

### Step-by-Step Solution:

1. **Understanding Van Niel's Experiment**:
- Van Niel conducted experiments using purple and green sulfur bacteria to understand the process of photosynthesis. He concluded that photosynthesis is a light-dependent process.

2. **Key Components of the Experiment**:
- The equation he proposed for the photosynthesis process in these bacteria is:
\[ \text{H}_2\text{S} + \text{CO}_2 \xrightarrow{\text{light}} 2\text{S} + \text{CH}_2\text{O} + \text{H}_2\text{O} \]
- In this equation, H2S acts as the hydrogen donor, which is crucial for the fixation of carbon dioxide (CO2) to produce carbohydrates.

3. **Identifying the Statements**:
- The statements provided about Van Niel's experiment need to be evaluated for correctness:
1. The experimental organism is purple and green sulfur bacteria. (Correct)
2. Sulfur compound is used by bacteria as the source of hydrogen. (Correct)
3. In photosynthesis, carbon dioxide splits to produce free oxygen. (Incorrect)
4. He used carbon dioxide and H2S as substrates. (Correct)

4. **Finding the Incorrect Statement**:
- The third statement is incorrect because, in photosynthesis, carbon dioxide does not split to produce free oxygen. Instead, it is fixed to form carbohydrates, while water is the source of oxygen.

5. **Conclusion**:
- Therefore, the incorrect statement about Van Niel's experiment is:
**In photosynthesis, carbon dioxide splits to produce free oxygen.**