Does average mass depend on the number of particles in the sample? What are the advantages and disadvantages of using the "average-of-averages"
mass to calculate the expected mass of 100 particles?

Abbreviated as mg-25.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.