What is the $BOD$ limit prescribed by the $CPCB$ for natural water bodies into which municipal waste is discharged?

Eutrophication of water bodies leading to the killing of fishes is mainly due to the non-availability of

Select the correct option for catalytic converters.

In a polluted lake,the index of pollution is

$A$ - Micro-organisms involved in the biodegradation of organic matter in the receiving water body consume a lot of oxygen,and as a result,there is a sharp decline in dissolved oxygen in the stream from the point of sewage discharge.
$R$ - $BOD$ decreases when the dissolved oxygen amount decreases in water.

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