The correct order of atomic radii in group 13 elements is

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Question

The correct order of atomic radii in group 13 elements is

Accepted Answer

Correct Answer: C — B Step-by-step Solution:In general, atomic radius increases down a group due to addition of new electron shells. However, Gallium (Ga) is an exception to this regular trend.Gallium follows the filling of 3d orbitals (10 electrons) in the transition series. These d-electrons offer poor shielding of the nucleus compared to s and p electrons. As a result, the effective nuclear charge experienced by the outermost electrons in Ga is higher than expected, pulling them closer to the nucleus.This makes the atomic radius of Ga (135 pm) smaller than that of Al (143 pm), even though Ga is below Al in the group.Actual values: B (85 pm) Why other options are incorrect:Options A and B place Al before Ga in increasing order, ignoring the d-block contraction effect that makes Ga smaller than Al.Option D incorrectly reverses the order of Tl and In.Key Concept: d-block contraction — when d-orbitals are filled before the element in question, poor shielding by d-electrons increases effective nuclear charge, resulting in a smaller atomic radius than the element above it in the same group. This is also observed for Tl (follows 4f filling) compared to In, though the effect is smaller.

The correct order of atomic radii in group 13 elements is

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The correct order of atomic radii in group 13 elements is

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