During discharge, nickel-cadmium batteries show a lower liquid level than at full charge because:

• A. The electrolyte becomes absorbed into the plates.
• B. A chemical action causes the electrolyte to evaporate through the vents.
• C. Current leakage from individual cells causes a rise in temperature.
• D. The electrolyte expands and spills out.

Answer: (A)

The key idea is that the plates in a nickel‑cadmium cell are porous and absorb electrolyte during operation. As the battery discharges, the chemical reactions convert the active materials into solid hydroxide compounds that take up water within the plate structure. This internal uptake pulls electrolyte out of the free space in the cell, so the visible liquid level drops compared with when the cell is fully charged. It isn’t due to evaporation, leakage, or heating effects—it’s the electrolyte being absorbed into the plates. When you recharge, the reactions reverse enough that some of that absorbed electrolyte is returned to the solution, often raising the level again.