Circle only those of the following reactions that are redox reactions:

K2CrO4 + BaCl2 ? BaCrO4 + 2 KCl

Cu+S ? CuS

AgNO3 + HCl ? HNO3 + AgCl

2 Na + 2 H2O ? 2 NaOH + H2

MgBr2 + 2 NaF ? MgF2 + 2 NaBr

2 CO + O2 ? 2 CO2

SO2 + H2O ? H2SO3