Approximately how many known derivatives of $CFC$ or $BFC$ (Bromofluorocarbons) are recognized as $ODS$ (Ozone Depleting Substances)?

Match the items in List-$I$ with the items in List-$II$ and select the correct answer from the given options:

List-$I$	List-$II$
$A$. Bleaching of paper	$I$. $CF_2Cl_2$
$B$. Eye irritant	$II$. $H_2O_2$
$C$. Freons	$III$. $Na_2AsO_3$
$D$. Herbicide	$IV$. $PAN$
	$V$. $CO_2$

The reagent used in the determination of the chemical oxygen demand $(COD)$ of a water sample is

The pollutants which come directly into the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?

The pair of gases responsible for acid rain are

Which type of pollution is caused by the spraying of $DDT$ on crops?