central carbon atom obeys the octet rule or has more or less than an octet?

The carbonate ion, or ##CO_3^(2-)##, has a total of 24 , 4 from carbon, 6 from each of the three oxygen atoms, and 2 additional ones.

Three equivalent , also called , can be drawn for the carbonate ion

The molecule's (you can pick any of the three structures shown above, since they're all equivalent) has a total of 8 lone pairs of electrons and 8 electrons.

As you can see, the central carbon atom has zero lone pairs of electrons and uses all its 4 to form bonds with three oxygen atoms: 2 single bonds and 1 double bond.

The carbon atom obeys the because it has 8 electrons in its valence shell, 2 for each bond it has with the oxygen atoms.