Substances that cause pollution or contaminate the environment are called .........

The acceptable level of carbon monoxide gas $(CO)$ in the atmosphere in $ppm$ level is

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

Chlorine atoms act as catalysts in the depletion of the ozone layer in the Earth's atmosphere. These chlorine atoms originate from which of the following?

Which of the following gases causes the depletion of the ozone layer in the upper atmosphere?

$SO_2$ pollution is indicated by