Consider the set of isoelectronic atoms and ions a2–, b–, c, d+, and e2+. which arrangement of relative radii is correct?

The term isoelectronic atoms means that if the given atoms are neutral, they would have the same number of electrons, which is relative to their sizes. Ions with positive charges are called cations, losing electrons. On the other hand, ions with negative charges are called anions, gaining electrons. The more electrons that the atoms have, the bigger it is in size. Hence, the arrangement of the radii of the atoms would have to be,

      e²⁺, d⁺, c , b⁻, a⁻

The arrangement is from smallest to largest.