Answer:
True
Explanation:
According to Aufbau's principle "sublevels with lower energies are filled up before those with higher energies".
Sublevels do not fill up in numerical order but there is a certain manner in which they are filled. The pattern is shown below:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p e.t.c
We see that the 4s gets filled before the 3d sublevel.
