The charge to mass ratio(z/e) of the given species is given as follows:
O2- = z/e = 8/10 = 0.8
N3- = 7/10 = 0.7
F- = 9/10 = 0.9
Mg2+ = 12/10 = 1.2
Na+ = 11/10 = 1.2
Al3+ = 13/10 = 1.3
Now, higher the z/e, smaller is the atomic radii.
Thus, the atomic radii follows the order given below:
Al3+ < Mg2+ < Na+ < F- < O2- < N3-
Therefore, Optioin(4) is correct.
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