The electrolyte used in the Nickel-Iron (NiFe) accumulator is

1. Analyze the question The question asks which electrolyte is used in a Nickel-Iron (Edison) accumulator. This is a question on secondary cells in the topic of Current Electricity or Chemical Effects of Current.

2. Explain the concept There are two main types of rechargeable (secondary) cells you need to know:

• Lead-acid accumulator: The electrodes are lead and lead(IV) oxide. The electrolyte is dilute tetraoxosulphate(VI) acid (H₂SO₄). This is the one in car batteries.
• Nickel-Iron (Edison) accumulator: The electrodes are iron (negative plate) and nickel oxide (positive plate). The electrolyte is an alkali, potassium hydroxide (KOH) solution.

3. Step-by-step reasoning

• Option A (dilute H₂SO₄) is the electrolyte for the lead-acid cell, so it is wrong here.
• Option B (barium chloride) is a salt solution that is not used in accumulators.
• Option D (sodium hydroxide) is also an alkali, but the standard electrolyte in the Edison NiFe cell is potassium hydroxide, so it is not the textbook answer.
• Option C (potassium hydroxide solution) is correct. It is an alkaline electrolyte, which is why the NiFe cell is also called an alkaline accumulator.

4. Answer The correct option is C. potassium hydroxide solution.

5. Exam tip Remember: "Lead = Acid, Edison = Alkali."

• Lead-acid cell → dilute H₂SO₄
• Nickel-Iron (Edison) cell → KOH

Also note that the alkaline cell is lighter and more durable, but it has a lower e.m.f. (about 1.2 V per cell) than the lead-acid cell (about 2 V per cell).