A. a balanced chemical equation that includes the enthalpy change and phase of each reactant and product
Option A is the correct answer. A correctly written thermochemical equation should include a balanced chemical equation that represents the stoichiometry of the reaction, and it should also include the enthalpy change (ΔH) associated with the reaction. Additionally, it is common to include the phase (solid, liquid, gas, aqueous) of each reactant and product to provide a more complete representation of the reaction conditions. The phase information helps specify whether the substances are in gaseous, liquid, or solid form during the reaction. The entropy change (ΔS) and temperature change (ΔT) are not typically included in a thermochemical equation, although they may be relevant in certain contexts.