When a huge amount of sewage is dumped into a river,the $BOD$ will

Which of the following statements is incorrect?

In municipal sewage,$BOD$ values (in $ppm$) are

Explain tropospheric pollution in $100$ words.

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:

Have you ever observed any water pollution in your area? What measures would you suggest to control it?