Answer:
Heat
Explanation:
In chemical reactions no matter is created, instead the chemicals react and any new substance formed is made from a rearrangement of the chemicals put into it. E.g. CH4 +2O2 --> CO2 + 2H2O, if you count it the number of atoms of each element doesn't change.
Sunlight. Chemical reactions can release energy in the form of light but sunlight is light from the sun
Pollution: This isn't a main concern in chemical reactions, however unneeded waste can be disposed of.
This leaves heat. An exothermic reaction is one that releases heat. An example is yeast and peroxide
