10 percent solution means the solute is only 10% in the solution, so taking the volume of the solvent 100 ml then the mass of the solute will be either 10 gram or 10 ml. For example, 10% solution of sodium chloride (NaCl) means 10 grams of sodium chloride is mixed in 100 ml of water.
200mg=0.2g
0.2 x10=2ml