What happens when a zinc rod is placed in aqueous copper sulphate solution?

Correct Answer: The blue colour of the copper sulphate solution fades.

Step-by-Step Explanation:

1. Understanding the Chemical Reactivity:
Zinc (Zn) is more reactive than copper (Cu) according to the electrochemical series (reactivity series of metals). When a strip or rod of zinc is placed in an aqueous solution of copper sulphate (CuSO₄), a single displacement reaction occurs.

2. Chemical Reaction:
Zinc displaces copper from the copper sulphate solution, forming zinc sulphate (ZnSO₄) and solid copper metal (Cu):

${\text{Zn (s)}}_{}+{\text{CuSO}}_4\text{(aq)}\to {\text{ZnSO}}_4\text{(aq)}+\text{Cu (s)}$

3. Visual Changes Observed:
- Aqueous copper sulphate (CuSO₄) solution is blue in colour due to the presence of Cu²⁺ ions.
- As the reaction progresses, Cu²⁺ ions are reduced to copper metal (Cu), which deposits on the zinc rod as a reddish-brown coating.
- Zinc is oxidized to colorless Zn²⁺ ions, forming zinc sulphate (ZnSO₄) solution.
- Consequently, as Cu²⁺ ions are consumed, the blue colour of the copper sulphate solution gradually fades and eventually becomes colourless.

Therefore, the correct observation is that the blue colour of the copper sulphate solution fades.