Which of the following is a redox reaction?NaCl + KNO3 → NaNO3 + KClCaC2O4 + 2HCl → CaCl2 + H2C2O4Mg (OH)2 + 2NH4Cl → MgCl2 + 2NH4OHZn + 2AgCN → 2Ag + Zn(CN)2

To determine which of the given reactions is a redox reaction, we need to identify the changes in oxidation states of the elements involved.

1. NaCl + KNO3 → NaNO3 + KCl In this reaction, the oxidation states of sodium (Na) and potassium (K) remain unchanged, while the oxidation state of nitrogen (N) changes from +5 in KNO3 to +5 in NaNO3. Therefore, this reaction is not a redox reaction.

2. CaC2O4 + 2HCl → CaCl2 + H2C2O4 In this reaction, the oxidation state of calcium (Ca) remains unchanged, while the oxidation state of carbon (C) changes from +3 in CaC2O4 to +4 in H2C2O4. Therefore, this reaction is a redox reaction.

3. Mg(OH)2 + 2NH4Cl → MgCl2 + 2NH4OH In this reaction, the oxidation states of magnesium (Mg) and nitrogen (N) remain unchanged. Therefore, this reaction is not a redox reaction.

4. Zn + 2AgCN → 2Ag + Zn(CN)2 In this reaction, the oxidation state of zinc (Zn) changes from 0 to +2, while the oxidation state of silver (Ag) changes from +1 in AgCN to 0 in Ag. Therefore, this reaction is a redox reaction.

Therefore, the redox reactions among the given options are:

• CaC2O4 + 2HCl → CaCl2 + H2C2O4
• Zn + 2AgCN → 2Ag + Zn(CN)2