Answer:
Suffix -ous
Explanation:
The anions with a suffix -ite came from an oxide with one of the lower valence of the element. For example [tex]SO_3^-[/tex] is sulfite and came from the [tex]SO_2[/tex] where the S has a valence of +4)
Acids derived from those anions have the suffix -ous. For example [tex]H_2SO_3[/tex] is the sulfurous acid.