Answer: trigonal planar
Explanation: CO3^2- (carbonate) has 24 valence electrons (C 4 + O 3×6 + 2 extra = 24). The Lewis resonance structures put carbon at the center with three oxygens around it: one C=O double bond and two C–O single bonds where the singly bonded oxygens each carry a negative formal charge. Carbon bears a +1 formal charge in each resonance form, and the two singly bonded oxygens are each -1, giving overall charge -2.
Because the three resonance forms are equivalent, the real structure is a resonance hybrid with three equal C–O bonds of bond order 1⅓. Carbon is sp2 hybridized with no lone pairs, giving an AX3 electron-domain geometry and molecular shape of trigonal planar (approx. 120° bond angles).