Oxygen evolved during photosynthesis comes from

Options

A. `CO _(2)`
B. `H _(2)O`
C. `CO _(2) and H _(2)O`
D. salts

Answer

**Step-by-Step Solution:**

1. **Understanding Photosynthesis**: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose. The overall equation for photosynthesis can be represented as:
\[ 6CO_2 + 12H_2O \xrightarrow{\text{light} + \text{chlorophyll}} C_6H_{12}O_6 + 6O_2 + 6H_2O \]

2. **Identifying the Source of Oxygen**: In the photosynthesis equation, oxygen (O2) is produced as a byproduct. To determine where this oxygen comes from, we need to analyze the reactants involved.

3. **Role of Water (H2O)**: Water (H2O) is one of the reactants in the photosynthesis equation. During the light-dependent reactions of photosynthesis, water molecules are split (a process known as photolysis) to release oxygen.

4. **Mechanism of Oxygen Production**: The splitting of water occurs in Photosystem II (PSII), which is located in the thylakoid membranes of chloroplasts. When light is absorbed by chlorophyll in PSII, it energizes electrons, which leads to the splitting of water molecules:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]
Here, the oxygen produced is released into the atmosphere.

5. **Conclusion**: Therefore, the oxygen that is evolved during photosynthesis primarily comes from the splitting of water molecules, not from carbon dioxide (CO2) or any other source.

**Final Answer**: The oxygen evolved during photosynthesis comes from H2O (water).

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