The correct answer is b) enthalpy.
Enthalpy is a thermodynamic quantity that reflects the amount of heat content in a system at constant pressure. During a chemical reaction, bonds are broken and formed, which involves a change in energy. This change is typically measured in terms of enthalpy. When reactants transform into products, the change in enthalpy (ΔH) indicates whether the reaction absorbs heat (endothermic) or releases heat (exothermic). Thus, the heat exchange associated with a chemical reaction is fundamentally linked to the enthalpy of the materials involved.