JEE MAIN - Chemistry (2024 - 5th April Morning Shift - No. 7)
Given below are two statements:
Statement I: In group 13, the stability of +1 oxidation state increases down the group.
Statement II : The atomic size of gallium is greater than that of aluminium.
In the light of the above statements, choose the most appropriate answer from the options given below :
Explanation
Statement I:
"In group 13, the stability of +1 oxidation state increases down the group."
Analysis:
Group 13 Elements:
Boron (B)
Aluminum (Al)
Gallium (Ga)
Indium (In)
Thallium (Tl)
Common Oxidation States:
The typical oxidation state for group 13 elements is +3.
However, due to the inert pair effect, the +1 oxidation state becomes more stable as we move down the group.
Inert Pair Effect:
The reluctance of the s-electrons (ns²) in the valence shell to participate in bonding.
This effect becomes more significant in heavier elements due to poor shielding by inner d and f orbitals.
Stability Trend:
Boron (B): Exhibits only the +3 oxidation state.
Aluminum (Al): Predominantly +3 oxidation state.
Gallium (Ga): +3 is more stable, but +1 oxidation state starts appearing.
Indium (In): +1 oxidation state becomes significant.
Thallium (Tl): The +1 oxidation state is more stable than the +3 oxidation state.
Conclusion for Statement I:
Correct.
The stability of the +1 oxidation state increases as we move down group 13 due to the inert pair effect.
Statement II:
"The atomic size of gallium is greater than that of aluminium."
Analysis:
Expected Trend:
Generally, atomic size increases down a group because each successive element has an additional electron shell.
Actual Atomic Radii:
Aluminum (Al): Approximately 143 picometers (pm)
Gallium (Ga): Approximately 135 pm
Anomalous Behavior:
**Gallium's atomic radius is *slightly smaller* than that of aluminum.**
This anomaly is due to the presence of 10 d-electrons in gallium's electron configuration (Ga: [Ar] 3d¹⁰ 4s² 4p¹).
Poor Shielding Effect:
3d electrons do not shield the nuclear charge effectively.
As a result, the effective nuclear charge increases, pulling the outer electrons closer to the nucleus.
This causes gallium to have a smaller atomic radius compared to aluminum.
Conclusion for Statement II:
Incorrect.
The atomic size of gallium is less than that of aluminum due to poor shielding by d-electrons.
Final Answer:
Statement I is correct, as the stability of the +1 oxidation state increases down group 13.
Statement II is incorrect, because gallium has a smaller atomic radius than aluminum.
Answer: Option B
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