Which of the following cells does not require a dipolar for effective and efficient delivery of current?

Analyze the question: The word "dipolar" is almost certainly a typo for depolarizer. The question asks which cell does not need a depolarizer to deliver current effectively.

Concept: polarization in cells

• In some primary cells, hydrogen gas collects on the positive electrode during use. This hydrogen layer increases the internal resistance and reduces the current. The effect is called polarization.
• A depolarizer is an oxidizing agent that removes the hydrogen, usually by oxidizing it to water.

Check each option:

• A. Daniel cell: Copper sulphate solution acts as the depolarizer. It stops hydrogen forming by depositing copper instead. So it needs one.
• B. Dry Leclanché cell: Manganese(IV) oxide (MnO₂) is the depolarizer. So it needs one.
• C. Nickel-iron accumulator: This is an alkaline secondary (rechargeable) cell. It uses a KOH electrolyte and works through reversible redox reactions at the electrodes. No hydrogen builds up on the plates, so it needs no depolarizer.
• D. Voltaic cell: The simple voltaic cell (Zn and Cu in dilute H₂SO₄) has no depolarizer, so it suffers badly from polarization. It would need one for good delivery of current.
• E. Wet Leclanché cell: MnO₂ is the depolarizer. So it needs one.

Answer: The nickel-iron accumulator is the only cell in the list that does not require a depolarizer.

Tip: Remember these pairings:

• Leclanché cells use MnO₂.
• The Daniel cell uses CuSO₄.
• Accumulators (secondary cells) don't need a depolarizer.
• The simple voltaic cell is the one that suffers polarization.