Question

why green leaf change black in presence of sunlight?

Answer 1

Main function of the leaf of a tree is photosynthesis.This process helps the plants to prepare their own food.A green pigment called chlorophyll is needed for this process.With the presence of sunlight and chlorophyll leaves make food.Chlorophyll gives green color to the leaves.Chlorophyll are more concentrated 

Answer 2

that's because the green leaf loses its moisture due to the sunlight.
the sunlight absorbs all the essential elements which makes the green part of the leaf.
thus the green leaf changes into black in presence of sunlight