Q.Explain the effect of pressure on the solubility.

Solubility of a solute is the maximum amount that can dissolve in a specific amount of solvent at a given temperature; once reached, further solute cannot dissolve and simply stays undissolved -- the solution is saturated. Standardised measure: grams of solute per 100 g of solvent at a given temperature, forming a saturated solution.

Nature of solute and solvent ("like dissolves like"): ionic NaCl dissolves in polar water but not non-polar benzene; different gases dissolve to different extents in the same solvent (ammonia more soluble than oxygen in water).

Effect of temperature -- solid in liquid: solubility generally increases with temperature (higher kinetic energy helps break the solute's intermolecular forces). At saturation, $\text{Solute(solid)} \rightleftharpoons \text{Solute(dissolved)}$; by Le Chatelier's principle, raising temperature favours dissolution if it is endothermic, disfavours it if exothermic. NaCl's solubility barely changes with temperature (~10% rise 0-100$^\circ$C); NH$_4$NO$_3$ (endothermic dissolution) rises steeply; ceric sulphate (exothermic) actually falls; CaCl$_2$ (exothermic) still rises moderately because entropy also matters. …