Question

Although metals form basic oxides, which of the following metals form an amphoteric oxide?

• A. $\mathrm{Na}$
• B. $\mathrm{Ca}$
• C. $\mathrm{Al}$
• D. $\mathrm{Cu}$

Answer 1

The correct option is C

$\mathrm{Al}$

Metals form basic oxides and non-metals form acidic oxides. But few metal oxides show acidic as well as basic behaviour.

Amphoteric oxide: An amphoteric oxide is an oxide that can act as an acid or as a base. Examples are aluminium oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ and zinc oxide $\left(\mathrm{ZnO}\right)$.

The amphoteric behaviour of ${\mathrm{Al}}_2{\mathrm{O}}_3$ can be seen in the reactions given below. When it reacts with a base, it acts as an acid and vice-versa.

$$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3+6\mathrm{HCl}\stackrel{}{\to }2{\mathrm{AlCl}}_3+3{\mathrm{H}}_2\mathrm{O} \\ \left(\mathrm{base}\right)\left(\mathrm{acid}\right)\left(\mathrm{salt}\right)\left(\mathrm{water}\right) \end{gathered}$$

$$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3+2\mathrm{NaOH}\stackrel{}{\to }2{\mathrm{NaAlO}}_2+{\mathrm{H}}_2\mathrm{O} \\ \left(\mathrm{acid}\right)\left(\mathrm{base}\right)\left(\mathrm{salt}\right)\left(\mathrm{water}\right) \end{gathered}$$

Hence, the correct option is (C).