Which of the following situations most clearly demonstrates a key characteristic of a redox reaction?
- A. Water boiling to steam
- B. Hydrogen gas reacting with chlorine to form hydrogen chloride gas
- C. Sodium chloride dissolving in water
- D. Ethanol evaporating at room temperature
Explanation
Hydrogen goes from zero to plus 1 and chlorine from zero to minus 1, so electrons are transferred and oxidation numbers change, which is the defining feature of a redox reaction. Boiling, dissolving and evaporating are physical changes in which no oxidation number moves at all. Checking oxidation numbers on both sides is the reliable test.
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