It refers to the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.

Which one of the following statements is true?

Observe the figure and answer the following questions.
$(i.)$ What ecological term is used to describe the $DDT$ accumulation at different trophic levels?
$(ii.)$ List any one effect of $DDT$ accumulation on birds.
$(iii.)$ Will $DDT$ accumulation lead to eutrophication?
$(iv.)$ Does it affect the $BOD$?
$(v.)$ Name a disease caused by the accumulation of any heavy metal.

$SO_{2}$ pollution is indicated by

The dental disease characterized by mottling of teeth due to the presence of a specific chemical in drinking water is caused by which of the following elements?

Ahmed Khan's company developed a fine powder of recycled modified plastic called $..........$.