Introduction:
Acid rain refers to the deposition of acidic substances in the form of rain, snow, fog, or sleet. It is primarily caused by the pollution of the environment, particularly the release of certain gases into the atmosphere. Among the options given, the correct answer is option 'D' - Nitrous oxide and sulphur dioxide.

Explanation:
Nitrous oxide (NOx):
- Nitrous oxide is a greenhouse gas that is released into the atmosphere through various human activities such as fossil fuel combustion, industrial processes, and agricultural practices.
- It is a byproduct of the combustion of fossil fuels in vehicles, power plants, and industrial processes.
- Nitrous oxide can combine with water in the atmosphere to form nitric acid, which contributes to the acidity of acid rain.

Sulphur dioxide (SO2):
- Sulphur dioxide is another major contributor to acid rain.
- It is released into the atmosphere primarily through the combustion of fossil fuels, particularly those containing high levels of sulfur such as coal and oil.
- Industrial processes such as smelting, refining, and manufacturing also release sulphur dioxide.
- When sulphur dioxide reacts with water and oxygen in the atmosphere, it forms sulphuric acid, a highly corrosive acid that is a major component of acid rain.

Formation of Acid Rain:
- When nitrous oxide and sulphur dioxide are released into the atmosphere, they undergo chemical reactions with water, oxygen, and other compounds to form nitric acid and sulphuric acid, respectively.
- These acids can then combine with water droplets in the atmosphere to form acid rain.
- Acid rain can fall directly onto the Earth's surface or can be carried long distances by wind before being deposited.

Effects of Acid Rain:
- Acid rain has detrimental effects on the environment and human health.
- It can harm aquatic ecosystems by lowering the pH of lakes, rivers, and streams, making them uninhabitable for many aquatic organisms.
- It can also damage forests and vegetation by leaching essential nutrients from the soil and causing nutrient imbalances.
- Acid rain can corrode buildings, statues, and infrastructure made of materials such as limestone and marble.
- In addition, it can contribute to respiratory problems in humans and animals when the acidic pollutants are inhaled.

Conclusion:
Acid rain is primarily caused by the pollution of the environment with nitrous oxide and sulphur dioxide. These gases undergo chemical reactions in the atmosphere to form nitric acid and sulphuric acid, which then combine with water to form acid rain. The effects of acid rain are widespread and can have detrimental impacts on the environment and human health. It is crucial to reduce the emissions of these pollutants to mitigate the occurrence and effects of acid rain.