What is the full form of $COD$?

Identify the reactions that occur in photochemical smog.
$(i)$ $CH_2=O + H_2 \longrightarrow CH_3OH$
$(ii)$ $NO_{2(g)} \xrightarrow{h \nu} NO_{(g)} + O_{(g)}$; $O_{(g)} + O_{2(g)} \longrightarrow O_{3(g)}$
$(iii)$ $CH_4 + 2O_3 \longrightarrow CH_2=O + 2H_2O$
$(iv)$ $NO_{(g)} + O_{3(g)} \longrightarrow NO_{2(g)} + O_{2(g)}$

Match List-$I$ with List-$II$ :

List-$I$ (Species)	List-$II$ (Maximum allowed concentration in ppm in drinking water)
$A$. $F^{-}$	$I$. $< 50 \, ppm$
$B$. $SO_{4}^{2-}$	$II$. $< 5 \, ppm$
$C$. $NO_{3}^{-}$	$III$. $< 2 \, ppm$
$D$. $Zn$	$IV$. $< 500 \, ppm$

The chemical added to leaded petrol to prevent the deposition of lead in the combustion chamber is

Environmental pollution is the effect of undesirable changes in the properties of our air,land,water,or soil that may harmfully affect...

Two statements are given below.
Statement-$I$: In dry cleaning,the solvent $Cl_2C=CCl_2$ was earlier used and now it is replaced by liquified $CO_2$.
Statement-$II$: In bleaching of paper,$H_2O_2$ was used earlier and now it is replaced by chlorine gas.
Correct answer is