When plants and animals decay,the organic nitrogen is converted into inorganic nitrogen. The inorganic nitrogen is in the form of

Some statements are given:
$(S_1) \ CO_2$ is a greenhouse gas.
$(S_2)$ Classical smog contains smoke,fog,and a high concentration of $SO_2$.
$(S_3) \ DDT$ is biodegradable.
$(S_4)$ Drinking water should have a high $B.O.D.$
Which is the correct sequence of true $(T)$ or false $(F)$ regarding the above statements?

$A$ water sample has $ppm$ level concentration of following anions: $F^{-} = 10 \ ppm$,$SO_4^{2-} = 100 \ ppm$,$NO_3^{-} = 50 \ ppm$. The anion/anions that make the water sample unsuitable for drinking is/are:

Which solvent from the following is used in order to avoid the creation of waste and the pollution of air?

Which of the following statements about smog is correct?

Water samples with $BOD$ values of $4 \ ppm$ and $18 \ ppm$ respectively are: