$BHC$ and $DDT$ belong to which class of pesticides?

$A$ lake with an inflow of domestic sewage rich in organic waste may result in:

One of the human diseases due to biomagnification of heavy metals is

Identify $X$ and $Y$ from the figure representing an Electrostatic Precipitator:
$X-Y$

Differentiate between Brown air and Grey air.

Catalytic converters are fitted into automobiles to reduce the emission of harmful gases. Catalytic converters change unburnt hydrocarbons into