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Why is gallium described as an amphoteric element?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — boron group element Modern version of the periodic table of the elements (printable).

Gallium is described as an amphoteric element because it can react as either an acid or a base, depending on the chemical environment.1

This property is observed in its chemical behavior and the nature of its compounds:

Reactivity: Gallium metal reacts with mineral acids to form gallium ions ( $G a^{3 +}$ ) and dissolves in alkalies to produce gallates, such as $[G a (O H)_{4}]^{-}$ , while evolving hydrogen gas.1
Oxide Behavior: The oxide of gallium ( $G a_{2} O_{3}$ ) is amphoteric, meaning it can exhibit either acidic or basic characteristics depending on the conditions.2
Hydroxide: The gallium hydroxide compound, $G a (O H)_{3}$ , is also amphoteric and can be precipitated from solutions of gallium salts by using alkali hydroxides.1

In the context of the boron group, this amphoteric nature is shared with aluminum and indium, representing a transition in chemical character between the acidic boric oxide ( $B_{2} O_{3}$ ) and the purely basic thallic oxide ( $T l_{2} O_{3}$ ).2