Which of the following is NOT a redox reaction?
- A. Zn + 2HCl gives ZnCl2 + H2
- B. 2H2 + O2 gives 2H2O
- C. NaOH + HCl gives NaCl + H2O
- D. 2Mg + O2 gives 2MgO
Explanation
In neutralisation no element changes its oxidation number, since hydrogen stays at plus 1, oxygen at minus 2 and both sodium and chlorine keep their values throughout, so only ions are rearranged. In the other three reactions a metal or hydrogen changes from zero to a positive state while another element is reduced. Checking oxidation numbers on both sides is the reliable test.
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