The delicate balance of $CO_2$ and $O_2$ is $NOT$ disturbed by:

Smog is generally produced in the presence of which of the following?

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

$List-I$ (Pollutant)	$List-II$ (Source)
$A$. Microorganisms	$I$. Strip mining
$B$. Plant nutrients	$II$. Domestic sewage
$C$. Toxic heavy metals	$III$. Chemical fertilizer
$D$. Sediment	$IV$. Chemical factory

Choose the correct answer from the options given below:

The concentration of dissolved oxygen in water for the growth of fish should be more than $X \ ppm$ and the Biochemical Oxygen Demand $(BOD)$ in clean water should be less than $Y \ ppm$. $X$ and $Y$ in $ppm$ are,respectively:

What are the harmful effects of photochemical smog and how can they be controlled?

Why is it necessary to measure the $BOD$ value of water?