An anion carries negative charge. Why ?
When an atom forms an anion, it gets one or more electrons (from another atom) in its outer shell. As the number of electrons in the outer shell is increased, the repulsion between them increases. This makes the shell expand outward. Further, since the number of protons remains the same as in the neutral atom, the nucleus attracts the increased number of electrons less strongly. For these reasons the anion is bigger than the parent atom.