1. foam
2. sol
3. gel
4. solid sol
Best answer
Answer: 4. solid sol
Key idea: Name a colloid by its dispersed phase and dispersion medium.
Pumice stone is a solid that traps gas, so gas is dispersed in a solid. Many textbooks and coaching keys class this as a solid sol (option 4), while others call gas in solid a solid foam. Option 1 'foam' means gas in a liquid, which pumice is not, and gel (option 3) is a liquid in a solid.
The official NTA key is option 4. Honestly, the naming is not uniform across books, so a student could argue for 'solid foam', but that term is not offered, and option 4 is the closest official choice.
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