Carbon source is the answer for ur question
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The reason why boiling water is a physical change is because when water changes state there still the same ammount it is just in a different form.
Well physical would be if you have Clay and you molded into a new shape or if you put butter on your toes and it melts or water evaporating from the surface of the ocean chemical changes would be milk going sour jewellery tarnishing which means turning into a different color or rust bread putting it in the oven and turning it into toes or rust forming on the nail that is left outside
