After long storage, a nickel-cadmium battery shows a low liquid level. Which explanation is most consistent with this observation?

• A. The electrolyte evaporates
• B. The case has absorbed moisture
• C. Electrolyte becomes absorbed into the plates
• D. The electrolyte has chemically changed

Answer: (C)

The key idea is that in nickel-cadmium cells, electrolyte can move into the porous electrode plates during long storage. The plates wick and retain some of the potassium hydroxide electrolyte, so the free liquid at the top appears lower even though the total electrolyte hasn’t significantly left the cell. This redistribution is a normal aging effect and doesn’t indicate a leak or a chemical change of the electrolyte. Evaporation isn’t the right fit here because the cell is sealed and venting is minimal; moisture entering the case wouldn’t cause the internal level to drop; a chemical change would usually show other issues such as gas formation or performance loss. So, electrolyte becoming absorbed into the plates best explains the observed low liquid level after long storage.