Indicate the mass fraction (%) of potassium chloride, 120 g of solution of which contains 18 g of potassium chloride.

Potassium chloride: KCl.
The task is very simple, it can be solved in one action according to the formula: W = (m.r.v – va / mr – pa) * 100%.
Where mr.v-va is the mass of the solute (18g).
mr-ra is the mass of the solution (120 g).
We substitute the available data into the formula and we get: W = 18/120 * 100 = 15%.
Answer: the mass fraction of potassium chloride in the solution is 15%.