Which element will most readily react with sodium to form a compound

• A. Potassium
• B. Chlorine
• C. Helium
• D. Boron

Answer: (B)

Sodium tends to lose its one valence electron, while nonmetals that are highly electronegative readily gain electrons to complete their outer shell. Chlorine fits that perfectly: it has seven valence electrons and needs just one more to reach a full octet, so it eagerly accepts an electron from sodium. That electron transfer creates Na+ and Cl− ions that lock together in a strong, stable ionic lattice—sodium chloride. Helium is inert and won’t form compounds easily; boron can react with sodium but not to give the same simple, highly favorable salt; potassium would be another reactive metal, often forming alloys rather than a discrete compound with sodium. So chlorine is the element most readily forming a compound with sodium.