Which of the following chemical reactions represents a redox process?
AgNO3+KI→AgI+KNO3\text{AgNO}_3 + \text{KI} \rightarrow \text{AgI} + \text{KNO}_3AgNO3+KI→AgI+KNO3
K2Cr2O7+2KOH→2K2CrO4+H2O\text{K}_2\text{Cr}_2\text{O}_7 + 2\text{KOH} \rightarrow 2\text{K}_2\text{CrO}_4 + \text{H}_2\text{O}K2Cr2O7+2KOH→2K2CrO4+H2O
2FeCl3+H2S→2FeCl2+S+2HCl2\text{FeCl}_3 + \text{H}_2\text{S} \rightarrow 2\text{FeCl}_2 + \text{S} + 2\text{HCl}2FeCl3+H2S→2FeCl2+S+2HCl
MgCO3→MgO+CO2\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2MgCO3→MgO+CO2