If a leaf is first kept in darkness and then placed in light without carbon dioxide, what is expected in the starch test?

Correct answer: Very little starch or no starch will form

The dark period is used to destarch the leaf: stored starch is consumed in respiration. During the subsequent light period, photosynthesis still requires carbon dioxide as a raw material. Since carbon dioxide is absent, little or no new carbohydrate is produced, so iodine will not show the usual blue-black starch colour, or it will show it only weakly. Therefore option B is correct; the other statements contradict photosynthesis and plant physiology.