Which of these things does not show that a reaction has occurred? a the mixture gets hotter b the substance changes from a liquid to a solid. c the mixture changes colour. d bubbles of gas form in the mixture.

I believe it may be C. Because, the color changing has nothing to do with the reaction you get.

If my hypothesis is correct, the answer should be B. All answers, A, C, and D are chemical reactions. They are all reactions, but B does not fit the category, so they only answer could really be B. (I debated between both A and B because those are the only answers that can be correct)