Final answer:
The type of energy change that occurs in the reaction C + O → CO2 is Thermal to Chemical.
Step-by-step explanation:
The type of energy change that occurs in the reaction C + O → CO2 is (d) Thermal to Chemical. In this reaction, thermal energy is being converted into chemical energy. When the reactants C (carbon) and O (oxygen) combine to form the product CO2 (carbon dioxide), energy in the form of heat is released and stored in the chemical bonds of CO2.