Question

The correct order of atomic radii in group 13 element is:

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

Answer 1

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

Atomic and ionic radii of group 13 elements are lower than those of alkaline earth metals of group 2 primarily due to greater nuclear charge of group 13 elements as compared to group 2 elements. On moving down the group the atomic radius increases but atomic radius of $Ga$ is slightly lower than that of $Al$. This is due to the presence of d-electrons in $Ga$ which do not shield the nucleus effectively. As a result, the electrons in $Ga$ experience greater force of attraction by the nucleus than in $Al$ and hence the atomic radius of $Ga$ 135 pm is slightly less than that of $Al$ 143 pm. Thus, the increasing order of atomic radii of group 13 elements is $B<Ga<Al<In<Tl$.