Which of these correctly shows the group of atoms and/or ions in order of decreasing size?
Cu > Cu+ > Cu2+
Cu > Cu+2 > Cu+
Cu+ > Cu > Cu2+
Cu2+ > Cu+ > Cu

A. Cu>Cu+>Cu2+

Explanation:

Protons pull on the electrons surrounding them. If there are more protons than electrons (protons > electrons), this means that because there are so little electrons, the protons can pull at them with more force.

Because they pull on them with more force, the electrons will get closer to the nucleus. Since the electrons are much closer, or much "tighter" to the nucleus, they will shrink.

Cu : 29 protons, 29 electrons

Cu+ : 29 protons, 28 electrons

Cu2+ : 29 protons, 27 electrons

Cu2+ has 27 electrons and 29 protons. Because there are now more protons than electrons, the protons will pull the e closer, making the atom smaller. The same applies to the others.