Identify the oxides of Group 13 elements

The given oxides are:

• $\mathrm{B_2O_3}$
• $\mathrm{Al_2O_3}$
• $\mathrm{Ga_2O_3}$
• $\mathrm{Tl_2O_3}$

Recall the trend in Group 13

As we move down Group 13, the metallic character generally increases.

• Boron is a non-metal, so $\mathrm{B_2O_3}$ is acidic.
• Aluminium oxide $\mathrm{Al_2O_3}$ is amphoteric.
• Gallium oxide $\mathrm{Ga_2O_3}$ is also amphoteric, but a bit more basic than $\mathrm{Al_2O_3}$.
• Thallium is the most metallic among these, so its oxide shows the greatest basic character.

Reason using metallic character and oxide nature

In general:

• Non-metal oxides are acidic.
• Metal oxides are basic.
• As metallic character increases, basic character of oxides increases.

Therefore, the order of basicity is approximately:

Evaluate the options

• A: $\mathrm{Al_2O_3}$ → amphoteric, not most basic
• B: $\mathrm{Tl_2O_3}$ → most basic
• C: $\mathrm{B_2O_3}$ → acidic
• D: $\mathrm{Ga_2O_3}$ → amphoteric/basic but less basic than thallium oxide

Final answer

The most basic oxide is:

Comparison with stored correct answer

Stored correct answer: B

Our derived answer is also B.