Over $10 \ ppm$ fluoride causes

If the $pH$ of water increases above ......,the effectiveness of chlorination in water is reduced.

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

Which of the following statements is true about the ozone layer?

Match the following:

List-$I$ (Pollutant concentration limit in water)	List-$II$ (Effect)
$A. Pb > 50 \ ppb$	$I. \text{Liver damage}$
$B. SO_4^{2-} > 500 \ ppm$	$II. \text{Laxative effect}$
$C. NO_3^{-} > 50 \ ppm$	$III. \text{Blue baby syndrome}$
$D. F^{-} > 2 \ ppm$	$IV. \text{Brown mottling of teeth}$

The correct answer is

Ozone is considered an important component in the stratosphere because $......$