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Introduction to Pollution-
The contamination of the environment as a result of bad human activities is called Pollution.It is caused due to adding harmful gases,smoke into the air,fouling the water resources, and adding wastes into land.There are three types of pollutions- air pollution,water pollution,land pollution.Pollution is drastically increasing in all the countries due to increasing human activities and rising population.Pollution affects the nature, our health and endangers many valuable species.So there's an immediate requirement to minimize the pollution for  better health and save many of the valuable species and the nature.
Air pollution:
Air pollution causes due to the release of harmful gases or smoke in a large quantity from factories and industries.Now-a-days this pollution is drastically increasing due to the construction of industries in large numbers.However it's also caused due to some natural factors.When there's a forest fire,erupting volcanoes or radioactive decay of rocks a lot of harmful gases like carbon dioxide,chlorofluorocarbon, radon, etc.This gases greatly affect people's health.
Greenhouse effects is a natural process in which the greenhouse gases trap the heat inside the earth so that it remains warm during night.If greenhouse gases won't be trapping the heat in the atmosphere then earth would be a very cold place.The earth get energy from sun inform of sunlight.During the day all the things absorb the sun's energy through radiation and before all the heat escapes to outer space these gases absorbs some of it,so that we feel warm and comfortable during the night.But increse in these gases will pollute the atmosphere and thus cause global warming or rise in temperature.This change will cause floods, droughts and other natural disasters due to a problem in the balance in ecosystem.

How can we reduce air pollution ? 

Whenever it's possible use your bicycle or go for a bus.Plant trees in your neighbourhood and take care of them.Recycle glass bottles,cans,papers etc.(this conserves energy).DON'T burn leaves in your garden rather you can compost them.Reduce your amount of driving to reduce air pollution.Make sure that your car doesn't emit a lot of gas.Save power.Improve your fuel economy.

Water pollution:
Water pollution is caused by the contamination of water by the spilling of toxic chemicals into the water.Water pollution almost always means that some damage has been done to an ocean, river, lake, or other water source.Water pollution is also caused by the spilling of toxic chemicals into the water by factories, due to oil spills,various activities like washing clothes,bathing etc at river banks,or putting dead bodies of animals or human beings into the rivers etc. Groundwater pollution is much less obvious than surface-water pollution, but is no less of a problem. Water pollution is usually less obvious and much harder to detect than this. 

How to reduce water pollution ?

Don't dispose household wastes into the water sources. Dispose waste properly. Use the minimum amount of detergent and/or bleach when you are washing clothes or dishes.  Use only phosphate free soaps and detergents.Minimize the use of pesticides, herbicides, fertilizers. Don't dispose these chemicals, motor oil, or other a fluids into the sewer systems,because
they end at a river.Don't flush medications or trash into the toilet.Prevent soil erosion by planting more and more plants in the locality.Also help clean up litter in water filled areas.
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Thanks @Arnav..
Baap rey lipimishra..... Great work priyanshi
Tysm @adarsh
Great answer