Which one of the following statements is not valid for aerosols?

$A$ - 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.

Black foot disease is caused by the toxicity of which of the following?

According to the Euro $III$ norms,what was the controlled limit for sulfur content in petrol?

When domestic sewage mixes with river water,

Compared to normal water,the $BOD$ of sewage-polluted water is . . . . . . .