According to Class 9th Science chapter 2 notes, we solve the numerical as follows,

Mass of solute (NaCl) = 56 g

Mass of solvent (H2O) = 100 g

Mass of solution (NaCl + H2O) = 156 g

Concentration = Mass of solute/Mass of solution x 100

Concentration = 56/156 x 100 = 35.89%

Hence, the concentration of the solution is 35.89%

These topics can also be downloaded from Is Matter around us pure?  class 9 notes pdf download or Class 9 Science chapter 2 notes pdf download.