Decibel $(dB)$ is a standard abbreviation used for the quantitative expression of

Fluoride pollution primarily affects which of the following?

Define/Explain the following terms:
$(i)$ Eutrophication
$(ii)$ Jhum cultivation

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:

It is a common practice to undertake desilting of the overhead water tanks. What is the possible source of silt that gets deposited in the water tanks?

Catalytic converters,which have expensive metals as catalysts,are fitted into automobiles for reducing emission of poisonous gases. Which of the following is $NOT$ used in them?