Answer: Aufbau Principle
Step-by-step explanation:
Aufbau Principle - states that lower energy orbits must be completely filled before moving onto a higher energy level
Hund's Rule - pairing rule; all boxes in the level must be given one arrow before adding a second arrow
Pauli Exclusion Principle - each box must contain two arrows pointing in different directions
This question doesn't completely fill the 1s level before moving onto the next 2s level. Therefore, the digram violates the Aufbau Principle.