Gas emission is observed during charging of nickel-cadmium cells. Toward which part of the charging cycle is this observation characteristic?

• A. Toward the end of the charging cycle
• B. At the very start
• C. Throughout charging
• D. Only after full discharge

Answer: (A)

Gas emission during nickel‑cadmium charging signals that the cell is nearing full charge. As charging continues beyond what the cell can store, the excess energy drives electrolysis of water in the electrolyte, producing hydrogen and oxygen gas. This gassing begins toward the end of the charging cycle and becomes more noticeable if charging continues, indicating overcharge if not stopped. Early in charging, gas production is minimal because the cell is still accepting charge and the conditions for water electrolysis aren’t present. It’s not a feature of the entire charging process, nor something that would occur only after a complete discharge.