And there are several ways of expressing concentration...
"Molarity"="Moles of solute"/"Volume of solution"Molarity=Moles of soluteVolume of solution
"Molality"="Moles of solute"/"Kilograms of solvent"Molality=Moles of soluteKilograms of solvent
Now at LOW concentrations, generally, "molarity"-="molality"molarity≡molality...at higher concentrations (and different temperatures), the values diverge...
"Percentage by mass"="Mass of solute"/underbrace"Mass of solution"_"mass of solute + mass of solvent"xx100%..
You have to be able to interpret which concentration is quoted, and which is required...
There is also chi_"the mole fraction"="Moles of solute"/"Total moles in solution"