$A$ biosphere is composed of

Biochemical Oxygen Demand $(BOD)$ is the amount of oxygen required (in $ppm$):

Water filled in two glasses $A$ and $B$ have $BOD$ values of $10$ and $20$ respectively. The correct statement regarding them is:

Which of the following reactions is directly related to the corrosion of the Taj Mahal?

Fill in the blanks:
$(1)$ $A$ special cloud is formed over the Antarctica region in winter,which is called ..............
$(2)$ $A$ known source of pollution is called ..............
$(3)$ An unknown source of pollution is called ..............
$(4)$ The concentration of dissolved oxygen in water is ......... and the concentration of dissolved oxygen in air is ............

Use of chlorofluorocarbons is not encouraged because