用離子-電子法配平下列反應(yīng)式 (1)H2O2+Cr2(SO4)3+KOH→K2CrO4+K2SO4+H2O (2)KMnO4+KNO2+KOH→K2MnO4+KNO3+H2O (3)PbO2+HCl→PbCl2+Cl2+H2O (4)Na2S2O3+I2→NaI+Na2S4O6