Which of the following is a weightless pollutant?

Disadvantages of chemical agents are:
$I.$ Chemicals are toxic and harmful to human beings and animals.
$II.$ Chemicals pollute the environment and plants.
$III.$ Weedicides used to remove weeds also pollute the soil.
Choose the correct option.

In a eutrophic water body,the excessive growth of $\underline {X}$ leads to the death of $\underline {Y}$.

Which of the following is/are primary air pollutant$(s)$?

In a coal-based power plant,electrostatic precipitators are installed to control which of the following?

$BOD$ stands for ....