Question

The increasing order of atomic radii of the following elements is:

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

Answer 1

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

The atomic radius generally increases as we move down a group in periodic table. But due to poor shielding effect, d block contraction plays an important role for deciding the atomic radius of $Ga$ and basically due to d block contraction, the radius of $Ga$ is less than that of $Al$. Thus the correct increasing order of atomic radii is:
$Ga<Al<In<Tl$