What is the symbolic representation $dB$ used for?

According to the Euro-$III$ norms,what was the controlled limit for sulfur content in diesel (in $ppm$)?

Biochemical Oxygen Demand $(BOD)$ is a measure of:

Observe the figure and answer the following questions.
$(i.)$ What ecological term is used to describe the $DDT$ accumulation at different trophic levels?
$(ii.)$ List any one effect of $DDT$ accumulation on birds.
$(iii.)$ Will $DDT$ accumulation lead to eutrophication?
$(iv.)$ Does it affect the $BOD$?
$(v.)$ Name a disease caused by the accumulation of any heavy metal.

In a polluted lake:

$A$: Taj Mahal is being destroyed by $SO_2$ coming from Mathura refinery.
$R$: This converts $CaCO_3$ into unstable calcium sulphate.