3. What is the best explanation for the decrease in first ionization energy moving from Be to B? (A) Moving from Be to B, more electrons are added to the
atoms, thus increasing the electron-electron repulsions.

(B) Moving from Be to B, more protons in the nucleus
attract the valence electrons, making it harder to remove
the electrons.

(C) The electrons in Be are being removed from a full sub- shell, which is more stable than the half-filled sub-shell in B.

(D) The electrons in Be are located in the 2s subshell. These electrons penetrate closer to the nucleus than the 2p electrons in B.