First, caluclate the formula mass of Mg S2O3. This is add the masses of each element in the formula. Mg: 24.3 g/mol. S: 2 32.1 g/mol = 64.2 g/mol. O: 3 16 g/mol = 48 g/mol => formula mass = 24.3 g/mol + 64.2 g/mol + 48 g/mol = 136.5 g/mol. Second, calculate the number of moles using number of moles = mass in grams / formula mass = 205 g / 136.5 g/mol = 1.5 moles. Anser: 1.5 moles
