Assertion (A) Mg ²⁺ and Al ³⁺ are isoelectronic but the magnitude of ionic radius of Al ³⁺ is less than that in Mg ²⁺ . Reason (R) The effective nuclear charge on the outermost electrons in Al ³⁺ is greater than that in Mg ²⁺ . The correct option among the following is

Step-by-step solution

Higher the electrostatic attraction between nucleus and valence electron, smaller will be the size of the atom/ion. Electrostatic attraction is given by Z_ eff =Z-S where, Z= the number of protons in the nucleus of an atom or ion (the atomic number) and S= shielding from core electrons. In case of Al ³⁺ and Mg ²⁺ , they are isoelectronic species and thus have same number of electrons as 1 s^2, 2 s^2, 2 p^6 isoelectric series of atoms and ions with different numbers of protons (and thus different nuclear attraction,