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1. What is pollution?
Pollution is defined as the introduction of harmful materials into the . These harmful compounds are referred to as .
2. What is tarnishing? Give an example.
 metal surfaces and other articles lose their shining appearance due to chemical reactions on the surface. For example,  become black on exposure to atmospheric air and brass vessels that contain copper as one of the constituents develop a greenish layer on exposure to air for a long time.