Which of the following sublevels is filled last? 3d, 4s, 4p, 4d, 5s
A)3 d
B)4 s
C)4 p
D)4 d
E)5 s

Question

Quizplus · Accepted Answer

According to the Aufbau principle, electrons fill orbitals starting from the lowest-energy level to the highest. Within the same energy level, the sublevels fill in the order: s, p, d, f. However, for elements in the fourth and higher periods of the periodic table, the 3d sublevel (which has slightly higher energy than the 4s sublevel) fills after the 4s sublevel. Therefore, the 4d sublevel is filled after the 4s sublevel, making choice D the correct answer.

Which of the Following Sublevels Is Filled Last? 3d, 4s