Biochemical oxygen demand $(BOD)$ value can be a measure of water pollution caused by organic matter. Which of the following statements is correct?

$A.$ 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:

Photochemical smog is known as ...... smog.

Which of the following practices will not come under green chemistry?
$1$. Using soaps made of vegetable oils instead of synthetic detergents,whenever possible.
$2$. Using $H_2O$ for bleaching purposes instead of chlorine-based bleaching agents.
$3$. Using liquefied $CO_2$ for dry cleaning clothes and laundry.
$4$. Using plastic cans for neatly storing substances.

Give a brief explanation about the international standards for drinking water.

Write a short note on the effect of Global warming and Greenhouse effect on environment.