Photochemical smog is related to the pollution of

The measured $BOD$ values for four different water samples $(A - D)$ are as follows:
$A = 3 \, ppm; B = 18 \, ppm; C = 21 \, ppm; D = 4 \, ppm.$
The water samples which can be called as highly polluted with organic wastes,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.

Given below are two statements.
Statement $I$: The non-biodegradable fly ash and slag from the steel industry can be used by the cement industry.
Statement $II$: The fuel obtained from plastic waste is lead-free.
In the light of the above statements,choose the most appropriate answer from the options given below:

Match the following:
| List-$I$ | List-$II$ |
| :--- | :--- |
| $A$. Methemoglobinemia | $I$. $1 \ ppm$ of dissolved oxygen in water |
| $B$. Kidney damage | $II$. $1000 \ ppb$ of lead in drinking water |
| $C$. Bones and teeth damage | $III$. $BOD$ of drinking water is $2 \ ppm$ |
| $D$. Growth of fish is stopped | $IV$. $2000 \ ppm$ of nitrates in drinking water |
| | $V$. $50 \ ppm$ of fluoride in drinking water |

Methyl mercaptans are generated as waste from which industry?