What is the chemical change that occurs when a small electrical current is passed through a substance?

• A. Oxidation
• B. Ionization
• C. Electrolysis
• D. Reduction

Answer: (C)

Electrolysis is the chemical change that happens when an electric current is passed through a substance that can conduct ions. The energy from the current drives the decomposition of the compound at the electrodes, producing new substances. At the two electrodes, oxidation (loss of electrons) occurs at one side and reduction (gain of electrons) occurs at the other, with ions moving through the solution or melt to balance charges. This whole process is powered by electricity, making a chemical change rather than a simple physical one.

Oxidation and reduction describe the electron transfer parts of the process, but they are not by themselves the full change that happens when current is applied. Ionization refers to forming ions, which can occur in various contexts, but electrolysis specifically refers to using electrical energy to decompose a substance into new chemical species.