Methods of crystallisation from solution: Which set of strategies can induce crystallisation of a solute from its solution?

Introduction / Context:
Crystallisation is a cornerstone separation and purification technique in chemical and pharmaceutical processing. Engineers often control supersaturation by manipulating solvent removal, temperature, or solution composition to nucleate and grow crystals selectively.

Given Data / Assumptions:

• Solute has finite solubility in the solvent.
• No chemical reaction; only physical separation by phase change.

Concept / Approach:
Crystallisation requires supersaturation. Three common routes are: (1) evaporating solvent to increase solute concentration; (2) cooling (or heating, for retrograde cases) to reduce solubility; and (3) adding a second solute/antisolvent to reduce solubility of the target (salting-out or antisolvent crystallisation).

Step-by-Step Solution:

Verification / Alternative check:
Industrial crystallisers (evaporative and cooling types) and antisolvent crystallisation in pharma validate each route. Process selection depends on thermodynamics, kinetics, and impurity profile.

Why Other Options Are Wrong:

• (a), (b), (c) alone are incomplete—each is valid, but the best answer is that all apply.
• (e) is false because multiple standard methods exist.

Common Pitfalls:
Overcooling causing excessive nucleation and fines; evaporating too fast causing occluded impurities; using an inappropriate antisolvent leading to oiling out instead of crystallisation.

Final Answer:
All of the above (a), (b) and (c)