Which is the correct orbital diagram for carbon?

The first option

Explanation:

Carbon is a p-block element. It is the 6th element on the periodic table and therefore it has 6 electrons.

The sub-level notation is given as:

                             1s²    2s²       2p²

            The s-sublevel can only accommodate two maximum electrons because it has one orbital. This is why both 1s and 2s contains just two electrons each. When both sub-levels are filled, we have just 2 remaining electrons to fill the p-sublevel.    

The p-sublevel contains 3 orbitals and can accommodate a maximum of 6 electrons. But we have just 2 electrons. According to Hund's rule of maximum mulitiplicity, electrons will go into degenerate orbitals singly before paring up. Therefore, the first two orbitals in p-sublevel will receive an electron each.  

 This is why the first model fits.          

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