Question:
The correct order of metallic radius of Al, Ga, In, Tl is
The correct order of metallic radius of Al, Ga, In, Tl is
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Remember anomaly: Gallium is slightly smaller than aluminium because of d-block contraction.
Updated On: Jun 15, 2026
- \(Tl>In>Al>Ga\)
- \(Tl>In>Ga>Al\)
- \(In>Ga>Al>Tl\)
- \(Ga>In>Tl>Al\)
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The Correct Option is A
Solution and Explanation
Concept:
Normally atomic radius increases down group.
However due to d-block contraction and f-block contraction anomalies occur.
Group 13 elements:
\[
Al,Ga,In,Tl
\]
Expected increase downward but gallium becomes smaller than expected due to poor shielding by d electrons.
Step 1: Observe periodic trend. Normally \[ Al<Ga<In<Tl \] But d-block contraction affects gallium. Its size becomes slightly smaller than aluminium.
Step 2: Apply d-block contraction effect. Gallium has filled 3d electrons. These electrons shield poorly. Effective nuclear charge increases. Radius decreases. Thus \[ Ga<Al \]
Step 3: Final order. Thus order becomes \[ Tl>In>Al>Ga \] Correct option: \[ \boxed{A} \]
Step 1: Observe periodic trend. Normally \[ Al<Ga<In<Tl \] But d-block contraction affects gallium. Its size becomes slightly smaller than aluminium.
Step 2: Apply d-block contraction effect. Gallium has filled 3d electrons. These electrons shield poorly. Effective nuclear charge increases. Radius decreases. Thus \[ Ga<Al \]
Step 3: Final order. Thus order becomes \[ Tl>In>Al>Ga \] Correct option: \[ \boxed{A} \]
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