Question

why do leaves fall down from the tree when they turn into yellow

Answer 1

By the scarcity of water and sunlight, the pigment which is responsible for photosynthesis called chlorophyll is broken down and absorbed. As a result, yellow pigments become unmasked and leaves fall off.

Answer 2

They fall down from tree when their green pigment is over.So there is no need of it.So it falls down.