Oil and fats can clog the drains reducing its effectiveness in filtering water. In open drains, they block the pores in the soil and thus hamper the filtration by soil. Hence, oil and fats should not be released into the drain.

So, the correct answer is 'Disposal of oil in open drain'.

• Sheela's teacher said in her classroom that we should not dispose of motor oils and medicines in the drain because Motor oil and medicine hamper(prevent) the degradation process.
• Chemicals present in motor oil and medicine kill the microbes that facilitate degradation process.so do not throw them down the drain.
• So, the correct answer is 'Motor oil and medicine hamper(prevent) the degradation process.'.

• The chemical present in paints, Solvents, Insecticides, motor oils, medicines may kill microbes that help purify water. So do not throw them down the drain.
• Hence Paints can kill water purifying microbes.
• So, the correct answer is 'Paints'.

• All the cooking oils should not be thrown in drains because it can harden and block the pipes. In an open drain, the fats clog the soil pores reducing its effectiveness in filtering water. 
• Throw oil and fats in the dustbin.
• Hence Cooking oil should not be thrown down the drain because they block the drainage pipes.
• So, the correct answer is 'They block the drainage pipes'.

There are several source of water pollution like industrial effluents, sewage water, radiobiological pollutants etc. Alum is used to clarify water by coagulating soil or mud particles whereas chlorine makes water free from pathogenic bacteria.

Waste articles are sorted out by Rag pickers and then rag pickers sell the articles to the industries engaged in recycling. 

Physical removal of particles by filtration and sedimentation. Then the grit is removed by sedimentation. All solids that settle form the primary sludge and the supernatant forms the effluent. The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and the air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh-like structures).

• Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature.
•  Hence, Differential scanning calorimeter is used to study the thermal behaviour of water.
• So, the correct answer is 'Differential scanning calorimeter'.

With development and advancement, industries, factories and other establishments have become necessary reality, the pollution can be mitigated by adopting measures as to the treatment of waste at generating source before it is exposed in the environment, reducing the generation of waste material and recycling the waste over and again wherever possible. Preventing the discharge that contaminates the fresh drinking water source.