複選題31. Which of the following statements about periodic trends in electron affinity (EA) and ionization energy (IE) are correct? (A) First ionization energy generally increases from left to right across a period due to increasing effective nuclear charge (B) Electron affinity always becomes more negative down a group because atomic size increases (C) Noble gases have very low ionization energies because of their stable electron configurations (D) The first ionization energy of oxygen is lower than that of nitrogen due to electron-electron repulsion in the $2p$ orbitals (E) Halogens have small electron affinities because their valence shells are already nearly filled