Final answer:
The last electron for oxygen is found in the 2p sublevel, following the Aufbau principle for electron configurations.
Step-by-step explanation:
The last electron for oxygen can be found in the 2p sublevel. Oxygen has an atomic number of 8, meaning there are 8 electrons to place in its electron configuration. Following the Aufbau principle, which dictates the order in which sublevels and orbitals are filled, the electron configuration for oxygen begins with the 1s sublevel, followed by the 2s sublevel. The remaining electrons are placed in the 2p sublevel. According to Hund's rule, the 2p sublevel consists of three orbitals, hence the first three electrons occupy one orbital each, and the fourth electron pairs up with one of the previously placed electrons, resulting in an electron configuration of 1s² 2s² 2p⁴.