The correct order of atomic radii in group 13 , elements is
As we have learnt,
The size of elements increases down the group generally.
However in Group 13 elements, there is an anomaly in the size of Al and Ga due to the filling up of d orbitals in the fourth period elements which lead to a poorer shielding effect.
Due to this poor shielding offered by the d electrons, the size of Ga is lesser than that of Al because of greater effective nuclear charge felt by the valence electrons of Ga.
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