In an electrochemical cell, polarization is caused by

Correct answer: Hydrogen

Explanation: In simple galvanic cells with acidic electrolytes, H⁺ ions are reduced at the cathode to H₂ gas. Bubbles of hydrogen adhere to the electrode surface, forming a film that increases internal resistance and lowers the current. This buildup is called polarization. Depolarizers (e.g., MnO₂ in dry cells) are used to remove or convert the hydrogen.

• Chlorine — Not the typical cause of polarization in common cells.
• Oxygen — Not the principal gas responsible for polarization in these cells.
• Tetraoxosulphate(VI) acid — The electrolyte (H₂SO₄), not the cause of polarization.
• Hydrogen — Correct. Hydrogen gas bubbles on the cathode cause polarization.