Final answer:
The most stable ion among OCN-, ONC-, and NOC- using Lewis structures and formal charge considerations is OCN-, as it allows for the negative formal charge to reside on the most electronegative atom, oxygen, and minimizes the formal charge on other atoms.
Step-by-step explanation:
To determine which of the following ions is most stable using Lewis structures and formal charge, we need to evaluate each possibility. The stability of a molecule or ion is influenced by the distribution of formal charges. Stable structures have negative formal charges on the more electronegative atoms and positive formal charges on the less electronegative atoms. Since oxygen is the most electronegative atom in these compounds, we should see the best structure having a negative formal charge on the oxygen atom.
In the case of the thiocyanate ion analogs provided (OCN-, ONC-, NOC-), we should choose the structure that minimizes the formal charges with the negative charge on the most electronegative atom, which is oxygen in this case. Therefore, the order OCN- is the most likely to be correct because it allows oxygen to carry the negative charge and carbon and nitrogen to have formal charges closest to zero. This structure aligns with the concept that the most stable Lewis structure tends to have the least formal charge separation.