Answer: 1s2 2s2 2p4
Step-by-step explanation:
Recall the number of electrons an orbital can have:
s orbitals have 2, p orbitals have 6, d orbitals have 10, f orbitals have 14, and so on.
Oxygen in its neutral state would have 8 electrons.
To summarize the diagonal filling order, it goes from the least energy level to the most, and the orbital with the least amount of orbitals to the most.
So, the order for this will go from 1 and end at 2 (for energy level,) then s, s again (as energy level 1 has 1s orbital only,) and p.
So, the first energy level, 1s2 (2 electrons), leaves the remaining six electrons.
Completely fill the s orbital (another 2 electrons), and the remaining 4 electrons will be in the respective p orbital.
Thus, it is 1s2 2s2 2p4.