Methods used for purification of organic compounds are based on:

Step 1: Understand What Determines a Purification Method

The choice of purification method is not arbitrary — it depends on the physical and chemical properties of the compound being purified as well as the nature of the impurities present.

Step 2: Analyse Each Option

(a) Neither nature of compound nor nature of impurity ❌ Absolutely false. Every purification method is chosen specifically based on these factors.

(b) Nature of compound only ❌ Partially true but incomplete. For example, boiling point of the compound alone is used in simple distillation, but the difference from the impurity's boiling point is equally important.

(c) Nature of compound AND presence of impurity ✅ Correct. Purification methods are chosen based on:

• Physical properties of the desired compound (bp, mp, solubility, volatility)
• Nature and properties of the impurities (is it volatile? soluble in same solvent?)

Examples:

• Distillation: chosen when compound is liquid and has different bp from impurities
• Crystallisation: chosen when compound is solid and has different solubility from impurities
• Sublimation: chosen when compound can sublime but impurities cannot
• Chromatography: chosen when compound and impurities have different adsorption affinities

(d) Presence of impurity only ❌ Incomplete — the intrinsic properties of the compound are equally important.

Step 3: Conclusion

Answer: (c) Nature of compound and presence of impurity

Key Points to Remember:

• Every purification method exploits a difference between the desired compound and the impurity
• This difference could be in: bp, mp, solubility, volatility, adsorption strength, polarity
• There is no single universal purification method — the choice depends on both compound and impurity properties