The fragrance of flowers is due to the presence of some steam volatile organic compounds called essential oils. These…

Step 1: Properties of Essential Oils

Essential oils are steam-volatile organic compounds responsible for fragrance in flowers. Key characteristics:

1. Steam volatile (appreciable vapour pressure)
2. Generally insoluble in water at room temperature
3. Miscible with water vapour in the vapour phase
4. Heat-sensitive (decompose at elevated temperatures)

Step 2: Eliminate Wrong Options

(a) Crystallisation ❌ — Used for solid compounds by dissolving in a hot solvent and allowing recrystallisation on cooling. Essential oils are liquids — crystallisation is inapplicable.

(b) Distillation under reduced pressure ❌ — Used for very high-bp, heat-sensitive compounds that cannot be distilled at atmospheric pressure. While essential oils are heat-sensitive, they are volatile enough that vacuum distillation is unnecessary and impractical for large-scale extraction from plant material.

(c) Distillation ❌ — High temperature required would decompose the essential oils. Also inefficient for extracting oils embedded in plant tissue.

Step 3: Why Steam Distillation is the Correct Choice

(d) Steam distillation ✅

Principle: $P_{\text{oil}} + P_{\text{water}} = P_{\text{atm}}$

The mixture boils below 100°C, preventing thermal decomposition of the heat-sensitive oil.

Process:

1. Steam passed through crushed flowers → oil vaporises with steam
2. Mixed vapours condensed in a condenser
3. Condensate: oil layer + water layer (immiscible)
4. Oil separated from water using a separating funnel

Step 4: Conclusion

Answer: (d) Steam distillation

Key Points to Remember:

• Both conditions required: steam-volatile AND water-immiscible
• Examples: rose oil, lavender oil, eucalyptus oil, clove oil — all extracted industrially by steam distillation
• Operating temperature always < 100°C (key advantage over direct distillation)
• Separating funnel used to recover the oil from the condensate