Explain why a leaf kept in the light for 24 hours will turn an iodine solution blue-black, whereas a leaf kept in light for 24 hours and then in the dark for 24 hours will have no effect on an iodine solution

The leaf kept in the light will turn blue-black because of the presence of starch after photosynthesizing. The leaf in the dark could not photosynthesize, which would not create starch so the iodine solution will have no effect.

Explanation:

Iodine stains a blue black in the presence of starch

yes? sounds right, but you didn’t ask a question.