Stage 1: General Trend (Li → Ne)
1b. More protons/increased nuclear charge
1c. Electrons in same energy level / shell 1d. No extra/similar shielding
Stage 2: Deviation Be → B
2c. higher in energy than (2)s so weaker attraction
3b. 2 electrons in 2p need to pair
3c. pairing causes repulsion (do not award if it is clear reference to repulsion is in s orbital)