I2+2Na2S2O3→Na2S4O6+2NaI
20 ml of 0.3M(=0.3N) Na2S2O3 will react with (20)(0.3)(1000)(2) moles of I2 which is 0.003 moles or 0.006 equivalents. Thus there are 0.006 equivalents in 25 ml of H2O2, hence, its normality is 0.24 N and thus, the volume strength is 0.24×5.6=1.344.