Mercury cell used in hearing aid devices contains anode comprising of
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Zinc-mercury amalgam
The mercury cell (also known as the mercuric oxide-zinc battery), historically used in hearing aids for its stable 1.35 V output and long shelf life, has an anode made of zinc-mercury amalgam (Zn(Hg)). This amalgam prevents unwanted side reactions like hydrogen gas evolution and zinc corrosion in the alkaline electrolyte.
The cathode is a paste of HgO mixed with carbon or graphite, and the electrolyte is typically KOH (or NaOH) paste, often with ZnO.
Anode reaction: Zn(Hg) + 2OH⁻ → ZnO + H₂O + 2e⁻
Cathode reaction: HgO + H₂O + 2e⁻ → Hg + 2OH⁻