12. In a volumetric flask with a volume of 500 cm3, a solution was prepared from a sample of 2.106 g of caustic soda, and the volume of the solution was brought to the mark. Titration of 25.00 cm3 of this solution requires 24.50 cm3 of 0.1000 N. HCl solution. Calculate the percentage of Na2O in caustic soda.

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