Answer:
C. Endothermic because breaking bonds require energy
Step-by-step explanation:
The reaction as follows is given in this question:
Cl2(g) → 2Cl(g)
According to this equation, chlorine molecule (Cl2) is broken down into chlorine atoms (2Cl) by breaking the bonds that holds the two atoms in the molecule together. Breaking of chemical bonds require energy input to occur.
An endothermic reaction is a reaction in which energy is absorbed or used up rather than released. Based on this definition, the reaction involving the breaking of bonds in chlorine molecule is an ENDOTHERMIC REACTION because breaking bonds require energy.