Explanation:

- Option 1: Aluminium

- Aluminium is highly reactive.

- It combines readily with oxygen and other elements.

- Not found in free state in nature.

- Option 2: Copper

- Copper is less reactive compared to many other metals.

- Can be found in its native (free) state in the earth’s crust.

- Correct answer.

- Option 3: Sodium

- Very reactive metal.

- Reacts quickly with water and air.

- Found in nature as compounds, not free state.

- Option 4: Potassium

- Highly reactive metal.

- Like sodium, it quickly reacts with water and air.

- Found only in compound form in nature.