The chlorine free radical reacts with ozone to form a ..... free radical.

Which gas was responsible for the Bhopal gas tragedy in $1984$?

Which gas contributes the least to global warming?

Explain why sometimes foaming is seen in river water near the place where sewage water is poured after treatment?

Which of the following particle sizes is associated with lung diseases?

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 ............