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Aqueous acidity of an oxide is the acidity of that oxide in water as medium. It is decided based on the acidity of the metal oxides.

Acidity is determined based on the electropositivity of the metals. When we move down the group, it is very easy to lose valence electrons from the metal atom. This means that electropositivity is increased when we move down the group, thereby increasing the metallic character, as we know that metal oxides are basic.

The given oxides are of group 13 elements. But in the case of group 13 elements, metallic character is found to be decreasing from Al to In, because of its extra d electrons, which shield the outer electrons. So has more metallic character than Ga and In.

Generally, metal oxides are basic in nature. Aqueous acidity is based on the acidity of those oxide compounds. If Al has more metallic character than Ga and In, then $A{l}_2{O}_3$will be more basic than $G{a}_2{O}_3$which is more basic than $I{n}_2{O}_3$. Thus, the acidity will be more for $I{n}_2{O}_3$. Thus the increasing order of aqueous acidity is given below:

$I{n}_2{O}_3<G{a}_2{O}_3<A{l}_2{O}_3$