$DDT$ is a

It refers to the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.

The main source of $BOD$ in the Ganga river is .....

$A$ : $PAN$ is a secondary pollutant.
$R$ : $PAN$ is formed by interaction of nitrogen oxides and hydrocarbons in the absence of light.

$A$: Water hyacinth is one of the most invasive weeds.
$R$: It increases the dissolved oxygen of water.

Which of the following diseases is caused or aggravated by pollution?