Classical smog occurs in which of the following atmospheres?

Biochemical oxygen demand $(BOD)$ value can be a measure of water pollution caused by organic matter. Which of the following statements is correct?

Which of the following is a non-conventional source of energy?

Sulphur dioxide is one of the components of polluted air. $SO_{2}$ is also a major contributor to acid rain. The correct and complete reaction to represent acid rain caused by $SO_{2}$ is ..... .

Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity?

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: