How many molecules of ozone can be decomposed by one atom of chlorine?

What will happen if deer is missing in the food chain given below?
Grass $\rightarrow$ Deer $\rightarrow$ Tiger

State one important function of ozone layer in the atmosphere. How is it formed there? Which compounds are responsible for the depletion of ozone layer? How do these compounds enter into the atmosphere?

Which radiations are prevented from reaching the Earth by the ozone layer?

Which is the primary factor responsible for the depletion of the ozone layer?

In an ecosystem,rats feed on grains. Name the trophic level to which the rats belong.