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Q.
The correct order of atomic radii in group $13$ elements is
The p-Block Elements
Solution:
The atomic radii as well as ionic radii increases on moving down the group $13$ elements because of the successive addition of one extra shell of electrons.
However, there is an anomaly in case of atomic radius. Atomic radius of Ga is lesser as compared to that of $Al$. Gallium $(Ga)$ with electronic configuration, $[ Ar ]_{18} 3 d^{10} 4 s^{2} 4 p^{1}$ has extra $d$-electrons which do not screen the nucleus effectively.
Consequently, electrons of $Ga$ are more attracted by nucleus.
Thus, the increasing order of atomic radii of the group $13$ elements is $B (85\, pm )< Ga (135\, pm )< Al (143\, pm ) < In(167\, pm )< Tl (170\, pm )$.