The mohls leaf experiment was conducted to show that photosynthesis needs carbon dioxide.So KOH or potassium hydroxide was used because itĀ absorbs co2 and iodine was used because iodine when put on a leaf turns blue black if starch is present and if not it turns brown,thus making it easy to judge the presence or absence of starch.

hope this helps you....plzz mark as best if it really did