Which metal is not required to have its charge specified in the names of ionic compounds it forms?

Options for the question:

-  Ru

- Sc

- Pd

- Mg

- Fe

Mg

Explanation:

Generally in ionic compounds, metals are grouped into metals that form one cation and metals that form more than one cation.

- Metals that form only one cation: These metals are usually in groups 1–3, 12, and 13. The name of the cation of a metal that forms only one cation is the same as the name of the metal. For example, Na+ is the sodium ion, Ca2+ is the calcium ion, and Al3+ is the aluminum ion. These metals generally do not have their charge being specified because thy have just one charge only and mere seeing their name one is expected to know that, Examples include Magnesium oxide.

- Metals that form more than one cation: This behavior is observed for most transition metals, many actinides, and the heaviest elements of groups 13–15. In such cases, the positive charge on the metal is indicated by a roman numeral in parentheses immediately following the name of the metal. Thus Fe2+ is iron(II), Fe3+ is iron(III), Sn2+ is tin(II), and Sn4+ is tin(IV). Example is Scandium (III) chloride/ Due to their numerous oxidation states, the charge has to be specified.

Upon looking at the options, all the metals are transition metals - capable of forming more than one cation except magnesium (Mg). So Magnesium is the correct option.