What is $DDT$ among the following?

$CFCl_3$ is responsible for the decomposition of ozone to oxygen. Which of the following reacts with ozone to form oxygen?

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?

The reagent used in the determination of the chemical oxygen demand $(COD)$ of a water sample is

Match the pollutant in List-$I$ with its maximum permissible limit in drinking water given in List-$II$.

List-$I$	List-$II$
$(A)$ Lead	$(I)$ $500 \text{ ppm}$
$(B)$ Sulphate	$(II)$ $50 \text{ ppm}$
$(C)$ Nitrate	$(III)$ $50 \text{ ppb}$

Which of the following statements is wrong?