Which of the Following Reactions Is the Most Likely to Be

Which of the following reactions is the most likely to be exothermic?

A) CaCO₃(s) $\rightarrow$ CaO(s) + CO₂(g)
B) Ca(g) $\rightarrow$ Ca²⁺(g) + 2 e^-
C) Cl₂(g) $\rightarrow$ 2 Cl(g)
D) Cl(g) + e^- $\rightarrow$ Cl^-(g)
E) CaCl₂(g) $\rightarrow$ Ca²⁺(g) + 2 Cl^-(g)