Lead concentration in blood is considered alarming if it is

In which one of the following have the $BOD$ (Biochemical Oxygen Demand) of sewage $(S)$,distillery effluent $(DE)$,paper mill effluent $(PE)$,and sugar mill effluent $(SE)$ been arranged in ascending order?

What happens when nitrates and phosphates are added to a lake?

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?

$BOD$ is a measure of what?

$DDT$ is a