How does potential energy of a system change during an endothermic reaction?

Explanation:

During an exothermic reaction bonds break and new bonds form and protons and electrons go from a structure of higher potential energy to lower potential energy. During this change, potential energy is converted to kinetic energy, which is the heat released in reactions. In an endothermic reaction the opposite occurs.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.