Question

which best explains why ionization energy tends to decrease from the top to the bottom of a group?
the number of orbitals decreases.
the number of neutrons decreases.
electrons get closer to the nucleus.
electrons get farther from the nucleus.

Explanation:

Ionization energy is the energy required to remove an electron from an atom. In a group (vertical column) of the periodic table, as we move from top to bottom, the number of electron shells (energy levels) increases. This means the outermost electrons are in shells that are farther from the nucleus. The attractive force between the nucleus and the outermost electrons decreases with increasing distance. So, it becomes easier to remove an electron (lower ionization energy) as electrons are farther from the nucleus.

• The first option is wrong because the number of orbitals (shells) increases down a group.
• The second option is wrong because the number of neutrons generally increases down a group (as atomic mass increases with more protons and neutrons in most cases).
• The third option is wrong because electrons get farther from the nucleus, not closer, down a group.

Answer:

D. Electrons get farther from the nucleus. (Note: Assuming the options are labeled A - D as per typical multiple - choice, with the last option being the correct one. If the original labeling was different, adjust the label but the text "Electrons get farther from the nucleus" is the correct choice.)