The technique used for purification of steam volatile water immiscible substance is:

Step 1: Define the Two Key Requirements

A "steam volatile, water-immiscible substance" has:

1. Steam volatile — appreciable vapour pressure; can vaporise along with steam
2. Water-immiscible — does not dissolve in water; separates as a distinct layer after condensation

Step 2: Evaluate Each Technique

| Technique | Based On | Suitable? | |---|---|---| | Fractional distillation | Close boiling points of miscible liquids | ❌ | | Fractional distillation under reduced pressure | High-bp, heat-sensitive miscible liquids | ❌ | | Distillation | Boiling point differences between miscible/single-component liquids | ❌ | | Steam distillation | Steam-volatile + water-immiscible compounds | ✅ |

Step 3: Principle of Steam Distillation

$P_{\text{total}} = P_{\text{organic}} + P_{\text{water}} = P_{\text{atm}}$

The mixture boils at a temperature below 100°C, regardless of the individual boiling points. This prevents thermal decomposition of heat-sensitive organic compounds.

After condensation, the two immiscible layers separate — the organic compound is collected from the organic layer using a separating funnel.

Step 4: Conclusion

Answer: (d) Steam distillation

Key Points to Remember:

• Both conditions essential: steam-volatile AND water-immiscible
• Examples: aniline (bp 184°C), nitrobenzene, turpentine oil, essential oils
• Distillation temperature always < 100°C in steam distillation
• Recovery: condensate collected → layers separated using separating funnel