Answer is: C. exothermic reactions.
For example, the Haber process is procedure for the production of ammonia, in this process atmospheric nitrogen (N₂) is converted to ammonia (NH₃) and energy is released:
N₂ + 3H₂ ⇄ 2NH₃ ΔrH = -92 kJ/mol.
There are two types of reaction: endothermic reaction (chemical reaction that absorbs more energy than it releases) and exothermic reaction (chemical reaction that releases more energy than it absorbs).