Her3, the chlorine ion will hav the smallest radii as it has the most number of electrons.and protons than the rest.
While considering Al3+ and Na+, the number of electrons in both are same, but the number of protons are different.
Aluminum has more electrons than sodium.
Thus the electrons are more closely attracted by aluminum than in sodium ion.
Hence radii of aluminum ion will be samller than that of sodium ion
Hence the order is (2)
Na+ >Al3+ > Cl-