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JAMB Chemistry 1989 Question 25

Question 25

Redox Reactions

Which of the reactions below is NOT an example of a redox reaction?
I Fe + 2Ag+ → Fe2+ + 2Ag
II 2H2S + SO2 → 2H2O + 3S
III N2 + O2 ⇌ 2NO
IV CaCO3 → CaO + CO2

  1. A.I, II and III
  2. B.II and III
  3. C.III and IV
  4. D.IV only
Show the answer and explanation

Answer: D (IV only)

Explanation

In I, II and III oxidation numbers change. In the decomposition of CaCO3 every element keeps its oxidation number (Ca +2, C +4, O −2), so IV is not redox.