Final answer:
Calcium and iodine are most likely to form an ionic bond because ionic bonds typically occur between metals and nonmetals, which calcium and iodine are, respectively.
Step-by-step explanation:
The pair most likely to form an ionic bond is calcium and iodine. Ionic bonds generally form between metals and nonmetals due to the significant difference in electronegativity between the two. In this case, calcium (which is a metal from group 2) and iodine (which is a nonmetal from group 17) exhibit the characteristics required to form an ionic compound, with calcium likely giving up two electrons to achieve a noble gas electron configuration, and iodine accepting those electrons to fill its outer electron shell.