Which element is most likely to form a positive ion?

Sodium is an alkali metal, which means it has a single electron in its outermost shell. Elements in this category tend to lose this one valence electron easily in order to achieve a more stable electron configuration, similar to the noble gases with full outer shells. By losing that electron, sodium forms a positive ion (Na⁺) and thus becomes more stable.

This tendency to form positive ions is characteristic of metals, particularly those in Group 1 of the periodic table. Sodium's relatively low ionization energy allows it to lose its outer electron with minimal energy input, facilitating the formation of the Na⁺ ion in various chemical reactions. This process is fundamental in ionic bonding, especially in compounds formed between metals and nonmetals.