Final answer:
Lithium (Li) is most likely to lose its single valence electron and form a positively charged ion or cation (Li+). Chlorine (Cl) gains an electron to become Cl-, and Neon (Ne) typically does not form ions due to its stable electron configuration.
Step-by-step explanation:
To determine which element's atoms are most likely to lose valence electrons and form a positively charged ion, also known as a cation, we need to consider their position in the periodic table and their electron configurations.
Lithium (Li) is in group 1A, meaning it has one valence electron that it wants to lose to achieve the noble gas electron configuration. Thus, when Li loses one electron, it becomes Li+ with a 1+ charge. Similarly, Rubidium (Rb) from the same group will also tend to lose one electron and form a 1+ cation. However, Chlorine (Cl) is in group 7A, and it typically gains an electron to form a negatively charged ion, Cl-. Neon (Ne) is a noble gas with a full valence shell and is unlikely to form ions because it already has a stable electron configuration.
Therefore, the element most likely to lose valence electrons and form a positively charged ion among the options given is Lithium (Li).