Too tough.
:O:
  ..
 C::O:
  ..
  O:
  ..
plus add two electrons to the right O. Add a 2- charge to the ion. This is ONE resonance form. You can draw the other two by moving the double bond from the central O (where I have it) to the top or to the bottom O.
Check to see that there are 24 electrons.
Last one thanks
lewis dot for
CO3^2-
2 answers
You must add two electrons to the top O, two to the right O, and two to the bottom O. I count 18 on what I drew, and it will make 24 if you had those 3 sets of two each.