Differentiate between Brown air and Grey air.

Euro-$III$ norms stipulate that sulphur be controlled at ....... $PPM$ in diesel and $PPM$ in petrol.

Define $BOD$ (Biochemical Oxygen Demand).

$A$: Biomagnification of $DDT$ can enhance the decline in bird population.
$R$: $DDT$ causes thinning of eggshells and their premature breaking by disturbing calcium metabolism.

In agriculture,improper drainage of water leads to:
$I-$ The soil becomes waterlogged.
$II -$ The soil surface draws up salts from the water.
$III -$ Salts are deposited as a thin crust on the land surface.
$IV -$ Salts start accumulating around the roots of the plants.
$V -$ The increasing concentration of salts becomes favorable for crop growth.
$VI -$ It is highly beneficial for agriculture.
Which of the above statements are correct?

Prime contaminants leading to cultural or accelerated eutrophication are