Question

Which of the following statements are not correct?
i. Atomic radius of Ga is less than that of Al
ii. The order of ionization enthalpy of group 13 elements is B>Al>Ga>In>Tl
iii. Boron trioxide is amphoteric in nature

• A. ii, iii only
• B. i, iii only
• C. i, ii only
• D. i, ii, iii

Hint:

Remember the trends in atomic radius and ionization enthalpy down a group, and be aware of exceptions due to factors like poor shielding by \( d \) and \( f \) electrons. Also, recall the nature of oxides of Group 13 elements: Boron oxide is acidic, Aluminum and Gallium oxides are amphoteric, and Indium and Thallium oxides are basic.

Answer 1

The Correct Option is A

Let's analyze each statement: i.
**Atomic radius of Ga is less than that of Al.
** Generally, atomic radius increases down a group.
However, due to the poor shielding effect of the \( 3d \) electrons in Gallium (Ga), the effective nuclear charge experienced by the valence electrons in Ga is higher than expected.
This leads to a contraction in the atomic size of Ga, making its atomic radius slightly smaller than that of Aluminum (Al).
The order is Al>Ga.
Therefore, this statement is correct.
ii.
**The order of ionization enthalpy of group 13 elements is B>Al>Ga>In>Tl.
** The first ionization enthalpy generally decreases down a group due to increasing atomic size and shielding effect.
However, there are exceptions due to electronic configurations and effective nuclear charge.
The actual order for Group 13 is approximately B>Tl>Ga>Al>In.
The ionization enthalpy of Ga is higher than that of Al due to the poor shielding effect of the \( 3d \) electrons in Ga, leading to a higher effective nuclear charge.
The order given in the statement is incorrect.
iii.
**Boron trioxide is amphoteric in nature.
** Boron trioxide (\( B_2O_3 \)) is primarily acidic in nature.
It reacts with basic oxides to form borates and with water to form boric acid (\( H_3BO_3 \)).
While it can react with very strong acids under specific conditions, its acidic character is dominant.
Aluminum oxide (\( Al_2O_3 \)) and Gallium oxide (\( Ga_2O_3 \)) are amphoteric.
Therefore, this statement is incorrect.
The statements that are not correct are ii and iii.