Across Period 3, the first–ionization energy rises overall but dips at both Al and S. Which combination of factors best accounts for these two separate deviations?
a) Al: pairing of electrons within a 3p orbital increases repulsion; S: electron enters a higher-energy 3p subshell
b) Both Al and S: larger atomic radii than their preceding elements reduce nuclear attraction on valence electrons
c) Al: electron enters a higher-energy 3p subshell; S: pairing of electrons within a 3p orbital increases repulsion
d) Both Al and S: lower effective nuclear charge than neighboring elements reduces attraction on valence electrons