The correct option is Both A and R are true and R is the correct explanation of A
Explanation
Photosynthesis is a physicochemical process wherein green plants utilize light energy to synthesize organic compounds. A critical component of this process is the light-dependent reaction, which results in the evolution of oxygen.
Analysis of Assertion and Reason:
- Assertion (A) is Correct: Early experiments by Jan Ingenhousz demonstrated that in the presence of bright sunlight, small bubbles form around the green parts of aquatic plants. It was later confirmed that these bubbles consist of oxygen. This phenomenon is a visible indicator of active photosynthesis in an aquatic environment.
- Reason (R) is Correct: The release of oxygen occurs during the photochemical phase (light reaction) of photosynthesis. Light energy is absorbed by chlorophyll and used to split water molecules ($H_2O$) into hydrogen protons, electrons, and molecular oxygen ($O_2$). This process is known as the photolysis of water.
- Relationship: The formation of oxygen bubbles described in the Assertion is the direct physical result of the chemical process described in the Reason. The splitting of water molecules releases oxygen gas, which accumulates as bubbles in water. Therefore, R is the correct explanation for A.
Key Takeaway:
Oxygen evolved during photosynthesis comes from the photolysis of water, not carbon dioxide. In aquatic plants, this evolved oxygen manifests visibly as bubbles around green tissues during the day.