Question

Some metal oxides react with acid as well as base to produce salt and water, these are known as amphoteric oxides. The examples of amphoteric oxides are:

• A. \(Al_2O_3\) and \(SiO\)
• B. \(Al_2O_3\) and \(ZnO\)
• C. \(CuO\) and \(ZnO\)
• D. \(CuO\) and \(SiO\)

Hint:

The two most common amphoteric oxides in secondary school chemistry are:
- Aluminum Oxide [\(Al_2O_3\)] \(\to\) forms Aluminate.
- Zinc Oxide [\(ZnO\)] \(\to\) forms Zincate.
Remembering these two formulas is extremely useful.

Answer 1

The Correct Option is B

Step 1: Recall the definition of an amphoteric oxide.
An amphoteric oxide is unusual because it can behave as a base with an acid and as an acid with a base, giving salt and water either way.
Step 2: Test aluminium oxide both ways.
\[ Al_2O_3 + 6HCl \to 2AlCl_3 + 3H_2O \] \[ Al_2O_3 + 2NaOH \to 2NaAlO_2 + H_2O \] Since it reacts with both an acid and a base to give salt and water, $Al_2O_3$ qualifies as amphoteric.
Step 3: Test zinc oxide both ways.
\[ ZnO + 2HCl \to ZnCl_2 + H_2O \] \[ ZnO + 2NaOH \to Na_2ZnO_2 + H_2O \] $ZnO$ passes the same dual test, so it is amphoteric too. Copper oxide and $SiO$ do not show this two-way behaviour, so options involving them are ruled out.
Step 4: Conclude.
The amphoteric oxides among the choices are $Al_2O_3$ and $ZnO$. \[ \boxed{Al_2O_3\ \text{and}\ ZnO} \]