Answer:

It possesses less electrons than the parent atom, but the overall nuclear charge remains the same, resulting in greater attraction of electrons to the nucleus. Cations have smaller radii than their parent atoms.

One atom’s outermost orbit gains an electron to form an anion. Having more electrons than the parent atom reduces effective nuclear charge, while keeping total nuclear charge constant increases distance between nucleus and valence electrons as electron attraction to nucleus diminishes. Anions hence have bigger radii than their parent atom.