Question

Carbon dioxide is necessary for photosynthesis.The chemical used to remove this gas most effectively from entering a control apparatus is

• A. Distilled water
• B. Sodium carbonate
• C. Calcium oxide
• D. Potassium hydroxide solution

Answer 1

The correct option is D Potassium hydroxide solution

CO${}_2$ in photosynthesis acts as a carbon source. Mohl performed an experiment (called Mohl's half leaf experiment) to demonstrate the necessity of carbon dioxide for photosynthesis.This apparatus consists of a hiding mouthed bottle with a small amount of KOH solution. A plotted plant is kept in darkness for two days to remove starch. A leaf lamina of the plant is introduced into the bottle in such a way that half of the leaf lamina is inside the bottle and half outside. The part inside bottle does not get CO${}_2$ because available CO${}_2$ is absorbed by KOH. The part outside the bottle gets CO${}_2$. After a few hours of experiment, this very leaf is tested by iodine.The part of leaf outside becomes blue while part remaining in the bottle is colorless suggesting that, photosynthesis occurs only in the outside leaf which produces starch and this starch gives blue colour with iodine. Thus, potassium hydroxide can be used to remove CO${}_2$ gas. So, the correct answer is option D.