Which of the following is not a biological indicator of water pollution?

The most hazardous metal pollutant used in automobiles is .....

$2$-wheelers Bharat Stage-$III$ $(BS-III)$ norms were implemented throughout the country in:

Oil slick causes mass scale death of fishes due to

Given below are two statements:
Statement $I:$ In a scrubber,the exhaust from the thermal plant is passed through a spray of water or lime to remove gases like $SO_2$.
Statement $II:$ Particulate matter $(PM\,2.5)$ cannot be removed by a scrubber but can be removed by an electrostatic precipitator.
In the light of the above statements,choose the most appropriate answer from the options given below:

Presence of large amounts of nutrients in waters causes excessive growth of....