28.728%
We are given;
Moles of the solute, C12H22O11 = 0.21 moles
Molar mass of C₁₂H₂₂O₁₁ = 342 g/mol
Mass of the solvent water = 250 g
We need to calculate the percent by mass of a solution
Mass = Number of moles × Molar mass
Therefore;
Mass of solute = 0.21 moles × 342 g/mol
= 71.82 g
% by mass = (Mass of solute ÷ mass of the solution)× 100
= (71.82 g ÷ 250 g) × 100
= 28.728%
Therefore, the percent by mass of the solution is 28.728%