Which of the following pairs has almost same atomic radii? a) Aluminium and Gallium b) Beryllium and Magnesium c) Magnesium and Aluminium d) Boron and Beryllium .   Experts , Please give appropriate explanation to the answer with example and without providing any link.

Dear student,

Correct answer is (a) Aluminium and Gallium.
General atomic radii trend is : Atomic radii decreases across a period and increases down the group.
Moving from Al to Ga size should increase but they have similar atomic radii due to poor shielding effect of 3d electrons in Ga. d- orbital is more diffused therefore less effectively shield the strong positive charge of the nucleus. Thus outermost electrons are more strongly pulled by the nucleus; thereby decreasing the size of Gallium.


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