The mass fraction is found by the formula: u = A * n / M, where A is the relative atomic mass of the element, M is the relative molecular weight of the substance, n is the number of atoms of the element in the molecule of the substance (index). According to the periodic table, we determine A and M. A (K) = 39. M (K2SO3) = 39 * 2 + 32 + 16 * 3 = 158. Mass fraction of potassium: u (K) = 39 * 2/158 = 0.4937 … Percentage: 49.37%.
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