The graph below shows the variation in first ionisation energy across Period 3:
Which statement best explains why magnesium (Mg\text{Mg}Mg) has a larger first ionisation energy than aluminium (Al\text{Al}Al)?
Mg\text{Mg}Mg has a smaller atomic radius than Al\text{Al}Al, resulting in a stronger electrostatic attraction to its outer electrons.
The outer electron in Al\text{Al}Al is lost from a 3p\text{3p}3p subshell, which is higher in energy and better shielded than the outer electron of Mg\text{Mg}Mg in the 3s\text{3s}3s subshell.
Mg\text{Mg}Mg has a larger nuclear charge than Al\text{Al}Al, which binds its outer electrons more tightly.
There is greater spin-pair repulsion in the outer subshell of Mg\text{Mg}Mg than in that of Al\text{Al}Al.
