An unknown substance undergoes a chemical chance that gives off heat. which of the following is true

Its C,
First thing: Its a chemical change that means the substance before the reaction and after the reaction will be different.
Second thing: Whenever they say 'GIVES OFF' heat, that means the reaction in exothermic and that the heat is in the products. and whenever they say 'ABSORBS' or 'TAKES IN' heat, that means the reaction in endothermic and that the heat is in the reactants.
Hope this helps!

The reaction will shift to the right