With which of the following ions is not an oxyanion? how do you know this? co32 , cn , so42 , no

The  ion  which  is not an oxyanion  is   CN

Explanation

Oxyanion  are  ions with generic  formula AxO   where  A represent a chemical element   and O  represent   an oxygen  atom.  Most element  can  form an  oxyanion  meeting the condition of  octet  rule.CN  is not  an  oxyanion  because   it lack  oxygen atom.

Write the formula of the compound.
Write the numbers of each atom in the formula. Insert the relative atomic mass for each type of atom. Calculate the total mass for each element.
Add up the total mass for the compound.