Question

what will be the colour of the leaf before adding iodine solution?

Answer 1

In case of the experiment to test the presence/synthesis of starch in leaves, the leaf is decolourised with iodine before adding alcohol. Initially, leaf has green colour but when this leaf is dipped in warm alcohol solution, it becomes colourless. After adding iodine, it shows blue black colour on the portions that where exposed to sunlight as these regions could only photosynthesise, and hence, change to blue-black colour.