Answer :
Final answer:
The 4s sublevel is lower in energy than the 3d sublevel according to the Aufbau principle, making 4s the correct answer (A) to the question regarding which sublevel is lowest in energy.
Explanation:
According to the Aufbau principle, the 4s sublevel is slightly lower in energy than the 3d sublevel. The Aufbau principle dictates that electrons occupy orbitals in order of increasing energy, starting with those closest to the nucleus. In the context of potassium's electron configuration, for example, the electron fills the 4s orbital before the 3d because the 4s has lower energy.
In addition, it's important to note that the 4s orbital actually fills before the 3d in ground state atoms early in period 4 of the periodic table. However, in ions of the same elements, the 3d may be lower in energy than 4s. Ultimately, the correct answer to the question is that the 4s sublevel is lower in energy than the 3d, making option A) 4s the correct choice.
