Answer:
The answer is helium, I hope this is helpful :)
I believe the correct answer to this question is:
“Mixtures”
By definition, mixtures are combination of substances
which are not really chemically combined and hence separable by physical means.
There are two types of mixtures, homogeneous and heterogeneous, both are also
separable by physical means.
<span>This is as opposed to Compounds which are chemically
bonded and cannot be separated by physical means.</span>
What chemical reaction??? Very vague
Radon is <span>not a source of air pollution related to human activities</span>
