The depolarizing agent in a Leclanché cell is

Analyze the question: It asks which substance in a Leclanché cell removes the hydrogen bubbles that form at the positive electrode. That substance is called the depolarizing agent.

Concept: The Leclanché cell is a primary (non-rechargeable) cell. Its parts are:

• Negative electrode: zinc case
• Positive electrode: carbon rod
• Electrolyte: ammonium chloride (NH₄Cl) paste or solution
• Depolarizer: manganese (IV) oxide (MnO₂), also called manganese dioxide

Problem (polarization): As the cell works, hydrogen gas forms at the carbon rod. The bubbles coat the rod and insulate it. This raises the internal resistance and lowers the current, so the cell's output drops. This effect is called polarization.

Solution:

• Manganese (IV) oxide is an oxidizing agent, so it reacts with the hydrogen before it can build up on the rod.
• Reaction: 2MnO₂ + H₂ → Mn₂O₃ + H₂O
• Checking the options: • A. Powdered carbon is mixed in to improve conductivity, but it does not remove hydrogen. • B. Manganese (IV) oxide oxidizes the hydrogen, so it is the depolarizer. • C. The carbon rod is the positive electrode (the collector). • D. Ammonium is part of the electrolyte (NH₄Cl), not the depolarizer.

Answer: B. Manganese (IV) oxide.

Tip: Remember "MnO₂ Mops up hydrogen." The depolarizer is always the chemical that gets rid of the hydrogen bubbles. In the Leclanché cell, carbon conducts, zinc is the negative terminal, NH₄Cl is the electrolyte, and MnO₂ is the depolarizer.