Approximately how many known derivatives of $CFC$ or $BFC$ (Bromofluorocarbons) are recognized as $ODS$ (Ozone Depleting Substances)?

The maximum prescribed concentration of copper in drinking water is ........ $ppm$.

Which of the following factors will be responsible for skin-related diseases in the coming years?

$A.$ Ammonium salts produce haze in the atmosphere.
$B.$ Ozone is produced when atmospheric oxygen reacts with chlorine radicals.
$C.$ Polychlorinated biphenyls act as cleansing solvents.
$D.$ 'Blue baby' syndrome occurs due to the presence of excess nitrate ions in water.
Choose the correct answer from the options given below:

An increase in the concentration of $CO_2$ in the atmosphere will result in ........

Mention two ways to prevent acid rain.