Which lewis structure is correct ?
The one that has three double bonds with oxygen atoms is correct, you can see the structure exist in significant compounds like caros acid H2SO5.
The structure of first image with 2 Double bond ( S = O ) are present is the correct lewis structure.
Lewis structure of CO4 2- ion is
I don't think there is any CO4 2-.
Because C can only have 4 bonds and, no combination is giving me CO4 2- ion