Which of the following indicates a successful neutralization of a nickel-cadmium battery electrolyte spill?

A successful neutralization of a nickel-cadmium battery electrolyte spill is indicated by a color change of the indicating solution. This is because specific color indicators are used in neutralization processes to visually represent the pH level of the solution. When a spill is treated with a neutralizing agent, the change in pH will cause the indicating solution to alter its color, providing immediate visual confirmation that neutralization has occurred.

This color change signifies that the acidic or basic properties of the electrolyte have been effectively neutralized, confirming that it is no longer in a hazardous state. Monitoring pH levels through color change is a common and reliable method in chemical spill management.

Other methods, such as odor reduction, temperature drop, or visual clarity, may also occur during or after the neutralization process, but they do not provide a definitive or direct indication that the spill has been successfully neutralized. Color change is the most reliable and immediate indicator for assessing the success of the neutralization process.