Which layer of the atmosphere is closest to the Earth's surface?

The $BOD$ values for pure water and highly polluted water are respectively

Do you observe any soil pollution in your neighborhood? What efforts will you make for controlling the soil pollution?

Which of the following chemicals is not involved in photochemical smog formation?

The gas $A$ has very low reactivity and reaches the stratosphere. It is non-toxic and non-flammable but is dissociated by $UV$ radiations in the stratosphere. The intermediates formed initially from the gas $A$ are:

How is $SO_2$ an air pollutant?