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JAMB Chemistry 1986 Question 17

Question 17

Redox Reactions

Which of these represents a redox reaction?

  1. A.AgNO3 + NaCl → AgCl + NaNO3
  2. B.H2S + Pb(NO3)2 → PbS + 2HNO3
  3. C.CaCO3 → CaO + CO2
  4. D.Zn + 2HCl → ZnCl2 + H2
Show the answer and explanation

Answer: D (Zn + 2HCl → ZnCl2 + H2)

Explanation

In D zinc goes from 0 to +2 (oxidised) and hydrogen from +1 to 0 (reduced). In the other reactions no oxidation number changes.