Concept:The Nickel-Iron (NiFe) accumulator is an alkaline rechargeable battery, so it requires an alkaline electrolyte rather than an acidic one.
Explanation:In a NiFe accumulator, the active materials are nickel hydroxide and iron hydroxide.
The electrolyte must allow ion movement without reacting destructively with the electrodes.
Dilute tetraoxosulphate(VI) acid is used in lead-acid batteries, not in NiFe cells.
Barium chloride solution is not a suitable battery electrolyte for this system.
Potassium hydroxide solution,
KOH, is the standard electrolyte for NiFe accumulators.
It provides good ionic conductivity and supports the reversible chemical reactions in the cell.
Sodium hydroxide solution is less commonly used and does not give the same performance as
KOH in these batteries.
Answer:The correct option is C. potassium hydroxide solution.