Match the following:

List-$I$	List-$II$
$A$. Insecticide	$I$. $COD$
$B$. $K_2Cr_2O_7 / 50\% H_2SO_4$	$II$. $PAN$
$C$. Bleaching of clothes and paper	$III$. $Na_3AsO_3$
$D$. Eye irritant	$IV$. $BOD$
	$V$. $H_2O_2$

The correct answer is:

Fill in the blanks:
$(1)$ Carbon dioxide is found in the ................. layer.
$(2)$ $A$ high concentration of carbon dioxide is responsible for ................. .
$(3)$ ................. gas is used in air conditioners.
$(4)$ Acid rain causes damage to the ................. monument (wonder).

Give the details of the different layers of the atmosphere and briefly describe the substances present in them.

London smog is found in

Some statements are given:
$(S_1) \ CO_2$ is a greenhouse gas.
$(S_2)$ Classical smog contains smoke,fog,and a high concentration of $SO_2$.
$(S_3) \ DDT$ is biodegradable.
$(S_4)$ Drinking water should have a high $B.O.D.$
Which is the correct sequence of true $(T)$ or false $(F)$ regarding the above statements?

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