Group-13 elements react with O$$_2$$ in amorphous form to form oxides of type M$$_2$$O$$_3$$ (M = element). Which among the following is the most basic oxide?

We need to identify the most basic oxide among the Group 13 oxides of type M$$_2$$O$$_3$$.

To begin,

Group 13 elements are: B, Al, Ga, In, Tl. As we move down the group, the metallic character increases progressively. Boron is a non-metal/metalloid, aluminum is a metal with some non-metallic properties, and by the time we reach thallium, the element is strongly metallic.

Next,

There is a fundamental relationship in chemistry:

- Oxides of non-metals are typically acidic (e.g., B$$_2$$O$$_3$$ is acidic)

- Oxides of metals are typically basic (e.g., Tl$$_2$$O$$_3$$ is basic)

- Oxides of elements with intermediate character are amphoteric (e.g., Al$$_2$$O$$_3$$, Ga$$_2$$O$$_3$$)

From this,

Going down Group 13, as metallic character increases, the basicity of the oxides also increases:

$$ \text{B}_2\text{O}_3 \;(\text{acidic}) < \text{Al}_2\text{O}_3 \;(\text{amphoteric}) < \text{Ga}_2\text{O}_3 \;(\text{amphoteric}) < \text{In}_2\text{O}_3 \;(\text{basic}) < \text{Tl}_2\text{O}_3 \;(\text{most basic}) $$

Tl$$_2$$O$$_3$$ is the most basic oxide because thallium is the most metallic element in Group 13. Its oxide is predominantly ionic in character, and it reacts with acids to form salts -- a characteristic property of basic oxides.

The most basic oxide is Tl$$_2$$O$$_3$$.

The correct answer is Option 3: Tl$$_2$$O$$_3$$.