Which of the following is a redox reaction?
- NaCl + KNO3 → NaNO3 + KCl
- Mg(OH)2 + 2NH4Cl → MgCl2 + 2NH4OH
- CaC2O4 + 2HCl → CaCl2 + H2C2O4
- 2Zn + 2AgCN → 2Ag + Zn(CN)2
In all the three reaction there is no change in the oxidation states. These are simple inonic reactions.
But in 2Zn + 2AgCN → 2Ag + Zn(CN)2 there is a change in oxidation state. Ag gains electrons and Zn lose electrons therefore it is a redox reaction.
The correct option is D.