Question

the closer a valence electron is to the nucleus, the (higher/lower) the ionization energy will be. this means it will be (easier/more difficult) to remove the electron, making it less reactive. higher - easier lower - more difficult higher - more difficult lower - easier

Explanation:

Ionization energy is the energy required to remove an electron from an atom. When a valence electron is closer to the nucleus, it is more strongly attracted to the positively - charged nucleus. A stronger attraction means a higher ionization energy (more energy is needed to overcome the electrostatic force between the electron and the nucleus). And if more energy is needed to remove the electron (higher ionization energy), it is more difficult to remove that electron.

Answer:

higher - more difficult