$NO_2$ and $O_3$ react with unburnt hydrocarbons in polluted air to form .....

Given below are two statements :
Statement $I:$ The nutrient deficient water bodies lead to eutrophication.
Statement $II:$ Eutrophication leads to decrease in the level of oxygen in the water bodies.
In the light of the above statements,choose the correct answer from the options given below:

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

The secondary precursors of photochemical smog are

The $COD$ (Chemical Oxygen Demand) of a water sample is determined using:

Recent reports of acid rain in industrial cities are due to the effect of atmospheric pollution by