Sacrificial Anode Protection Steps:

• Iron corrodes via oxidation: Fe(s) → Fe²⁺(aq) + 2e⁻.
• Magnesium, more reactive (higher in reactivity series), oxidizes preferentially: Mg(s) → Mg²⁺(aq) + 2e⁻.
• Electrons from Mg reduce Fe²⁺ ions: Fe²⁺(aq) + 2e⁻ → Fe(s).
• Overall: Mg displaces Fe²⁺, protecting iron.

Why D is correct:

• Represents the redox displacement where Mg acts as sacrificial anode, oxidizing to protect Fe per electrochemical series.

Why the others are wrong:

• A: Iron ion reduction alone; ignores Mg's role in providing electrons.
• B: Magnesium ion reduction; impossible as Mg is more easily oxidized.
• C: Reverse reaction; causes iron oxidation, worsening corrosion.

Final answer: D