Question 63 of 87

Which of the following is Redox reaction?

1. 2CrO42- + 2H+ Cr2O72- + H2O

2. CuSO4 + 4NH3 Na2S4O6 + 2NaI

3. 2Na2S2O3 + I2 Na2S4O6 + 2NaI

4. Cr2O72- + 2OH- 2CrO42- + H2O