Which is a substance that could be found in air, water or soil that is harmful to humans or animals? a.) fossil fuelb.) pollutantc.) smogd.) carbon dioxide

Hello!

A substance that could be found in air, water or soil that is harmful to humans or animals is a Pollutant.

The other substances cannot be found in air, water or soil. Fossil fuels can only be found in soil, smog can only be found in the air, and carbon dioxide can be found in the water or air. 

Pollutants are substances that have harmful effects and damage the environment.  Some examples of pollutants are Carbon Monoxide (air), Lead (soil) and Insecticides (water). 

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Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.