Final answer:
Potassium (K) and iodine (I) are the elements most likely to form an ionic compound if allowed to react together. The resulting compound is potassium iodide (KI).
Step-by-step explanation:
The pair of elements most likely to form an ionic compound if allowed to react together is d. K and I. Potassium (K) is a metal and iodine (I) is a nonmetal. Metals tend to lose electrons and nonmetals tend to gain electrons during a chemical reaction. Therefore, potassium would lose one electron to form a positive ion (K+), and iodine would gain one electron to form a negative ion (I-). The resulting ionic compound would be potassium iodide, with the chemical formula KI.