The smog known as London smog is .....

The pair of gases responsible for acid rain are

$A$ farmer is using pesticides in his field. He uses the produce from his field as food for fish. He is told that the fish are not fit for human consumption because large amounts of pesticides were found in the fish cells. How is this possible? Explain.

Petroleum is a source of energy that is:

Given below are two statements:
Statement $I$: Chlorofluorocarbons breakdown by radiation in the visible energy region and release chlorine gas in the atmosphere which then reacts with stratospheric ozone.
Statement $II$: Atmospheric ozone reacts with nitric oxide to give nitrogen and oxygen gases,which add to the atmosphere.
For the above statements choose the correct answer from the options given below :

Pure water would have a $BOD$ value of