Answer:- .Variation of solubilities of some ionic solids with temperature Generally rise in temperature increases the solubility. This is due to expansion of holes or empty spaces in the liquid solvent. Generally 10°C rise in temperature, increases the solubility of solids two fold. Dissolution process may be endothermic or exothermic. The solubility of the substances like NaBr, NaCl, KCl, etc. changes slightly with the increase in temperature. The solubility of the salts like NaNO3, KNO3, KBr, etc. increases appreciably with the increase in temperature. The solubility of Na2SO4 first increases and after 30°C decreases with the increase in temperature.  This variation in solubility with temperature can be used to separate the salts from the mixture by fractional crystallisation.