Photochemical smog is related to the pollution of

Biochemical oxygen demand $(BOD)$ is a measure of organic materials present in water. $A$ $BOD$ value less than $5 \ ppm$ indicates a water sample to be:

Which of the following conditions in drinking water causes methemoglobinemia?

Which of the following is $FALSE$ regarding acid rain?

Explain in short: Effect of ozone depletion on environment.

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