$A.$ 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:

During a school field trip,a botany student visited a beautiful pond in a village and collected some plants. He observed that villagers were washing clothes there,and household waste was spoiling its beauty in some areas. After a few years,he revisited the pond and found it completely covered with algae,emitting a foul smell,and the water had become unusable. Can you describe this condition of the pond?

Which of the following is not a common component of photochemical smog?

The chemical added to leaded petrol to prevent the deposition of lead in the combustion chamber is

The pair of gases responsible for acid rain are

What are $X$ and $Y$ in the following reaction?
$CF_2Cl_2 \stackrel{UV}{\longrightarrow} X + Y$