"When grass is covered for three days with a black coloured polythene. it
becomes yellow in colour. Design an experiment to prove this phenomenon.
State observations and conclusions.

answer:

The grass under the colorless cellophane will grow best, as it receives the full spectrum of light. Plants growing under red light are thin and spindly, while the grass grown under blue light is short and stocky. Grass that doesn’t receive any light will eventually turn yellow

Explanation:

If you leave grass alone underneath a yogurt container, it will turn yellow. Why does this happen? While people go to the grocery store to buy food so that they can survive and grow, plants can make their own food through a process called photosynthesis. This process involves water, carbon dioxide, and light, and is controlled by chloroplasts, tiny organ-like structures (or organelles) that contain a green pigment called chlorophyll. Chloroplasts also contain other pigments like xanthophylls (yellow) and carotenes (orange).          (please let me know if this helps or not)