Freons or chlorofluoro carbons are responsible for depletion of the ozone layer in the upper strata of the atmosphere. They are used as propellants, aerosol spray caps, refrigerants, firefighting reagents etc. They are stable and chemically inert compounds. They absorb UV-radiation and break down liberating free atomic chlorine which causes decomposition of ozone through free radical reaction. This results in the depletion of the ozone layer.

Freon are mainly Freon-1 (CFCl₃) and Freon-12 (CF₂Cl₂). They form free radical of chlorine in presence of UV-radiation. Such free radical decomposes O₃ as follows: 

The dynamic equilibrium between ozone and oxygen is crucial for maintaining the ozone layer. The initial breakdown of ozone occurs due to the action of U-V radiations.

Both the microorganisms present in the soil and hemoglobin are sink for CO.

As the use of DDT increased, the insects got selected and hence developed resistance against the pesticide. This made them ineffective against the insects. The increased used of DDT lead to soil pollution.

PAN (Peroxy acylnitrate) and Peroxy benzoyl nitrate are responsible for forming smoke and fog i.e. smog.

Greenhouse effect is responsible for decrease in the level of the ground water.

Diphenhydramine commonly known as Benadryl, is an antihistamine which is mainly used to treat allergies. Histamine is released by the mast cells present in the body during several types of allergic reactions and to a lesser extent during some viral infections, such as the common cold. It also includes rash, itching, watery eyes, itchy eyes/nose/throat, cough, runny nose, and sneezing. It is also used to prevent and treat nausea, vomiting and dizziness caused by motion sickness.

• Chloramphenicol is an antibiotic useful for the treatment of a number of bacterial infections.
• Omeprazole is in a class of drugs called Proton Pump Inhibitors (PPI) that block the production of acid by the stomach. It’s used to treat gastric or duodenal ulcers, gastroesophageal reflux disease, erosive esophagitis, and hypersecretory conditions.
• Norethindrone is a synthetic progestational hormone with actions similar to those of progestrone but functioning as a more potent inhibitor of ovulation.

Any oxidizing agent can be used to treat water pollution. Out of the given option, K₂Cr₂O₇ is an oxidizing agent and therefore can be used for treating water pollution.

Mercury poisoning produces a crippling and often fatal disease called Minamata disease.