Very easy and only answer number 4 what word is supposed to be there

chlorophyll

Explanation:

the chlorophyll in the leaf absorbs all the colors of the radiation from sun but reflects only green colour. that is why we see green when we look at a leaf on a tree.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.