This concentration unit focuses on the solute as a percent (by mass) of the total solution. Since to weight of the total solution is not given, I will assume 100g, as an example.
One mole of K2SO3 will have potassium (2x39), sulfur (1x32), and oxygen (3x16) = 158g/mole
So 158g/mole x 0.0328mole = 5.2g
100g of solution - 5.2g os solute = 94.8g of water ÷ 18g/mple = 5.2 moles of water
the total moles present = 5.2 + 0.0328= 5.266
The w/w % will be 0.0325/5.266 = 0.623%
If the total weight of the solution is different than 100g, the percentage will be different.