Assertion (A) : `Na^+ and Mg^2+` ions are isoelectronic but the ionic radius of `Na^+` is greater than the of `Mg^2+`. Reason (R) : The effective nuclear charge of `Na^+` ion is less than that of `Mg ^2+` ion.

Assertion: Na^(+) and Al^(3+) are isoelectronic but the magnitude of the ionic radius of Al^(3+) is less than that of Na^(+) Reason: The magnitude of effective nuclear charge of the outer shell electrons in Al^(3+) is greater than in Na^(+)

(A) : Mg^(2+) and Al^(3+) are isolectronic but the magnitude of ionic radius of Al^(3+) is less than that in Mg^(2+) . (R ) : The effective nuclear charge on the outermost electrons in Al^(3+) is greater than that in Mg^(2+) .

IE_(1) of Na is less than that of Mg-explain.