Question

In the process of photosynthesis, the source of oxygen is:

• A. ${CO}_2$
• B. $H_{2}O$
• C. $C_6{H}_{12}{O}_6$
• D. none of these

Answer 1

The correct option is B $H_{2}O$

In the process of photosynthesis, the carbohydrates are synthesized from carbon dioxide and water in the presence of sunlight and chlorophyll with the release of oxygen. Source of liberated oxygen in the process of photosynthesis is water and not carbon dioxide. This was proved by Ruben and Kamen in 1957. They used radioactive isotope of oxygen (O-18) in water and found that oxygen liberated in the process was isotopically labelled. On the contrary when oxygen -18 in carbon dioxide was used, the evolved oxygen did not show radioactivity. Thus, the overall equation of photosynthesis is currently accepted as the one given above.

Thus, the correct answer is option B.