Which of the following statements correctly defines crystallisation?
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It is a process of obtaining pure solid in the form of its crystals from its solution.
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It is a process of separating the suspended particles from a liquid mixture by rotating the mixture at a high speed.
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It is a process of separating a sublimable volatile component from a non–sublimable impurity.
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It is a process in which a solid is obtained in an impure form from its solution.
Crystallisation is the process in which crystals of a pure substance are obtained by cooling its hot saturated solution. This technique is used for purification of inorganic/organic solids. This is based upon the principle that when a crystal is formed, it tends to exclude the impurities which remain in the solution. Centrifugation is the process of separating the suspended particles from a liquid mixture by rotating the mixture at high speed. This technique is based on the fact that denser particles are forced to the bottom and lighter particles stay at the top when spun rapidly. Sublimation is the process of separating a sublimable volatile component (i.e. substance which changes directly from solid to gas, without going through the intervening liquid state, on heating and vice-versa on cooling) from non–sublimable impurities whereas evaporation is the technique used to separate non–volatile components (solutes) dissolved in volatile solvents, i.e. in this technique, an impure solid is obtained from its solution.