Final answer:
The true statement of all atoms that are anions is that the atom has more electrons than protons.
Step-by-step explanation:
An anion is a negatively charged ion that is formed when an atom gains one or more electrons. So, of the given options, the statement that is true of all atoms that are anions is C) The atom has more electrons than protons. When an atom gains electrons, it increases the number of electrons compared to its number of protons, resulting in a negative net charge.