The correct answer is 2. Oxygen has 8 electrons, and according to the Aufbau principle, they fill up the energy levels starting from the lowest energy level (closest to the nucleus) and moving outward. In the case of Oxygen, the first energy level can hold a maximum of 2 electrons, so the first 2 electrons occupy this level. The remaining 6 electrons occupy the second energy level, which can hold a maximum of 8 electrons.
