Asap which of these is an indication that a chemical reaction has occurred? a. melting of a substance b. boiling of a substance c. formation of a precipitate d. freezing of a subtance

A chemical reaction would be something like a paper burning, a match lighting, etc. A physical reaction is just a change in the appearance. At least partially.

A, B and D are all physical changes. The substance is still that substance and it hasn't changed chemically. The change of state of matter is only a physical change because the substance is still the same as it was in the previous state.

So the answer would be C.

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