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

Dry hygroscopic agents can be termed as any substance that promotes and sustains a state of dryness in its vicinity. strong bases such as soda-lime, sodium hydroxide, and lithium hydroxide can remove carbon dioxide by chemically reacting with it.

Complete answer:
Study on photosynthesis started around 300 years ago. On the basis of what we have studied in our earlier classes, simple experiments have shown that chlorophyll (green pigment of the leaf), light and $\mathop {CO}\nolimits_{}$, are required for photosynthesis to occur.
The first Experiment was done to demonstrate light & chlorophyll is necessary for photosynthesis: Take a destarched potted plant having variegated leaves and cover 2-3 leaves with the black paper.
Expose the potted plant to sunlight for 1-2 hours. Pluck one covered leaf and one exposed leaf and test them for starch. The covered leaf does not show a positive starch test showing that photosynthesis cannot occur in the absence of light.
The exposed leaf shows blue and yellow parts where the blue colour or positive starch test occurs in the chlorophyll-containing parts.
second Experiment was done to demonstrate $\mathop {CO}\nolimits_2$, is necessary for photosynthesis (Moll's Half leaf experiment): A part of leaf was enclosed in a test tube containing some $\mathop {KOH}\nolimits_{}$ soaked cotton (which absorbs $\mathop {CO}\nolimits_2$), while the other half of leaf was exposed to air.
When the two halves of leaf were tested for starch, it was found that only the exposed part of leaf tested positive for starch. This showed us that $\mathop {CO}\nolimits_2$ is required for photosynthesis.

Hence, the correct answer is option (D)

Note: Carbon dioxide is essential for photosynthesis. Potassium hydroxide solution helps to remove this gas most effectively from entering a control apparatus. Like other alkali metals, potassium hydroxide gets combined with $\mathop {CO}\nolimits_2$ to form potassium carbonate.