Question

what is pollutant?how it cause?

Answer 1

Substances that bring about undesirable changes in the atmosphere are called pollutants.
Due to the human activities like dumping of wastes in the water,industrial wastes,carbon monoxide,use of poisonous gases in the industries etc., cause pollution in the atmosphere.
similarly,the use of DDT in agriculture,addition of pesticides and fertilizers in the soil also causes pollution.these are some variety of causes. 

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Answer 2

The substances which contaminate the atmosphere, land and water is called pollutant .The sources are factories , power plant ,automobile exhausts ,burning of fireworks ,population growth etc.... are the causes