When an atom of chlorine and an atom of hydrogen become a molecule of hydrogen chloride; a chemical bond is formed and energy is released. The correct option is C. This is because the chemical reaction that form hydrogen chloride from chlorine and hydrogen atom is an exothermic reaction which invloves evolution of heat to the tune of -185KJ/MOL. It can be seen from the negative sign that the energy change is negative, because heat is lost to the enviroment.