What is the correct sequence of atmospheric layers starting from the Earth's surface?

Identify the true $(T)$ and false $(F)$ statements regarding the disease known as fluorosis:
$(1)$ Fluorosis weakens teeth and bones.
$(2)$ Fluorosis is caused by fluoride concentrations greater than $2 \ ppm$ $(2 \ mg/L)$.
$(3)$ Fluorosis causes neuromuscular disorders.
$(4)$ Fluoride deficiency causes fluorosis.

Which of the following methods can be used to control water pollution?

Which region of the atmosphere is the domain of all living organisms?

The insecticide $DDT$ is considered as . . . . . .

Which of the following statements are correct?
a) $F^{-}$ ion concentration above $2 \ ppm$ causes brown mottling of teeth
b) The maximum limit of nitrate in drinking water is $400 \ ppm$
c) Depletion of ozone layer leads to cataract and skin cancer
d) The irritant red haze in the traffic is due to oxides of sulphur