Final answer:
The formula for the monoatomic cation for zinc is Zn²+, which reflects its divalent nature in compounds like ZnS and in aqueous solution.
Step-by-step explanation:
The formula for the monoatomic cation for zinc is Zn²+. Zinc typically forms a divalent cation when it loses two electrons. This is evident in various compounds, such as zinc sulfide (ZnS), where we see a 1:1 ratio between zinc ions and sulfide ions. In solution, zinc cations similarly have a charge of +2, as shown in the complete ionic and net ionic equations provided in reference materials. These zinc ions (Zn²+) can also form complex ions with other anions, such as hydroxide, to the form [Zn(OH)4]²-.