Mg + Pb$^{2+}$ →  Mg$^{2+}$ + Pb What is the cell notation for the cell reaction above?

Analyze the question: We need the correct cell notation (cell diagram) for the redox reaction Mg + Pb²⁺ → Mg²⁺ + Pb.

Concept: Cell notation is written as:

Anode (oxidation) electrode | anode ion || cathode ion | cathode electrode

• The single vertical line (|) shows a phase boundary (solid | solution).
• The double vertical line (||) shows the salt bridge.
• Oxidation (loss of electrons) occurs at the anode, written on the left.
• Reduction (gain of electrons) occurs at the cathode, written on the right.

Solution:

1. Oxidation: Mg → Mg²⁺ + 2e⁻. Mg is oxidised, so it is the anode (left side): Mg | Mg²⁺
2. Reduction: Pb²⁺ + 2e⁻ → Pb. Pb²⁺ is reduced, so it is the cathode (right side): Pb²⁺ | Pb
3. Join them with the salt bridge: Mg | Mg²⁺ || Pb²⁺ | Pb

Checking the options:

• A: Electrode and ion are in the wrong places (Mg | Pb²⁺ is wrong). ✗
• B: The cathode half is written backwards (Pb | Pb²⁺), and the ion should come first on the right side. ✗
• C: Mg | Mg²⁺ || Pb²⁺ | Pb ✓
• D: Uses Mg⁺ and Pb⁺, which are the wrong charges. ✗

Tip: Remember "An Ox, Red Cat": Anode = Oxidation, Reduction = Cathode. Write the anode on the left and the cathode on the right, and read the notation as: metal | its ion || other ion | other metal. Also check that the ion charges match the equation.