Question

The chemical compound used to prove that ${\mathrm{CO}}_2$ is essential for photosynthesis was

• A. KOH
• B. KCl
• C. NaCl
• D. none of these

Answer 1

The correct option is A KOH

KOH is a strong base. It was used in Mohl's half leaf experiment. In the experiment, a part of a leaf was inserted in a bottle containing KOH-soaked cotton/KOH solution and the other part of the leaf was kept outside the bottle exposed to the air. The part of the leaf which was exposed to KOH did not turn blue black when starch test was performed. This was because KOH absorbed all the ${\mathrm{CO}}_2$ present in the air around that part of the leaf . This prevented the leaf from preparing carbohydrates even when it was exposed to sunlight. The other part of the leaf which was exposed to ${\mathrm{CO}}_2$ in the air turned blue black when starch test was performed. This was because it was able to prepare carbohydrates in the presence of sunlight. This experiment helped to assert the importance of carbon dioxide in preparing food using the process of photosynthesis by the plants.
KCl and NaCl (salts) do not serve the same purpose as KOH.