Question

Write the correct order of atomic radii in group 13 elements:

• A. $B<Ga<Al<In<Tl$
• B. $B<Al<Ga<Tl<In$
• C. $Ga<Al<Tl<In<B$
• D. $B<In<Al<Tl<Ga$

Answer 1

The correct option is A $B<Ga<Al<In<Tl$

Down the group, for each successive member one extra shell of electrons is added. Atomic radius increases down the group. But, there is an exception. Presence of additional 10 d-electrons in Ga offer poor screening effect for the outer electrons which increases the force of attraction between the outermost electrons and nuclear charge, due to which the atomic radius of gallium decreases.
Hence, Ga has a lower atomic radius as compared to Al.
Hence, the correct order of atomic radii is (a)