Acid rain is caused by the presence of $X$ and $Y$ in air. $X, Y$ are respectively

$BOD$ values (in $ppm$) for clean water $(A)$ and polluted water $(B)$ are expected respectively:

The measured $BOD$ values for four different water samples $(A - D)$ are as follows:
$A = 3 \, ppm; B = 18 \, ppm; C = 21 \, ppm; D = 4 \, ppm.$
The water samples which can be called as highly polluted with organic wastes,are .... .

The acids responsible for acid rain are ......... .

How is $SO_2$ an air pollutant?

On which bases can non-viable particulates be classified?