Solubilty = number of molesVolume of solvent\; \frac{\text{number of moles}}{\text{Volume of solvent}}Volume of solventnumber of moles×1000\times 1000×1000
Number of moles of KCl = massMolar mass\; \frac{\text{mass}}{\text{Molar mass}}Molar massmass
Molar mass of KCl = 39 + 35.5 = 74.5 g/mol, mass = 25.0g
Number of moles of KCl = 2574.5\; \frac{25}{74.5}74.525 = 0.336 mole
Solubilty = 0.33680\; \frac{0.336}{80}800.336×1000\times 1000×1000
= 4.2 moldm3^{3}3