Some ionic compound names have roman numerals in them. What do those numerals mean?

The correct option is A They indicate the charge on the cation
Naming of ionic compound: Add a Roman numeral in parenthesis after the cation to denote the charge on the cation.
Example:
$Fe(OH{)}_3$ has correct name " Iron (III) hydroxide".
As Iron is the name of "Fe" element and being negative part $OH$ is written as "hydroxide" and as the charge of $Fe$ is $+3$, hence, in bracket the $III$ is written in roman.