Explain Trends Using Electron Configuration Practice Test

Neon (Ne) has electron configuration 1s2 2s2 2p6. Sodium (Na) has electron configuration Ne3s1. Neon has a much higher first ionization energy than sodium. Which electron-configuration feature best explains this difference?

Magnesium (Mg) has electron configuration Ne3s2 and chlorine (Cl) has electron configuration Ne3s2 3p5. Both are in period 3 (same number of occupied shells). Chlorine has a smaller atomic radius than magnesium. Which statement best explains this trend using electron configuration ideas?