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JEE Advanced levelSingle correct optionDifficulty 3 of 3sc148

Samples I to IV are emulsions. I mixes readily with water and conducts electricity well. II mixes readily with kerosene but not with water, and oil-soluble Sudan III colours the whole liquid. III is coloured uniformly by a water-soluble dye. IV has almost zero conductivity and mixes readily with kerosene. Which samples are water-in-oil (W/O) emulsions?

  1. AI and III only
  2. BI and IV only
  3. CII and III only
  4. DII and IV only

Answer: D

If the continuous phase is water the emulsion mixes with water, conducts and takes up water-soluble dyes uniformly. That applies to I and III, which are O/W. If the continuous phase is oil, the emulsion mixes with kerosene, conducts poorly and is coloured throughout by an oil-soluble dye, which fits II and IV (W/O).
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