The correct sequence of atmospheric layers starting from the Earth is:

Excess of which of the following in water causes blue baby syndrome disease?

What steps should be taken to reduce the production of acid rain?

Why is it necessary to measure the $BOD$ value of water?

Which of the following compounds is the most harmful component of photochemical smog?

Formation of photochemical smog involves the following reactions in which $A$,$B$,and $C$ are respectively:
$(i)$ $NO_2 \stackrel{h\nu}{\longrightarrow} A + B$
$(ii)$ $B + O_2 \rightarrow C$
$(iii)$ $A + C \rightarrow NO_2 + O_2$
Choose the correct answer from the options given below: