Q.91 Chemistry ⭐ 360° Option Elimination Active
NEET 2023 Chemistry Question 91 Solution
Topic: Surface Chemistry · Official NTA Booklet Code G5
Question
Pumice stone is an example of -
- (1)foam
- (2)sol
- (3)gel
- (4)solid sol
✓
Verified Against NTA Final Answer Key
Option (4) : solid sol
📚 Surface Chemistry Easy
📋 Given Parameters & Problem Setup
Substance Pumice stone
Dispersed phase Gas
Dispersion medium Solid
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⏱️ Save ~25 seconds The 30-Second Exam Hall Shortcut: ⚡ NCERT Colloid Table Anchor: Gas in Solid Medium = Solid Sol
Pumice stone is formed from volcanic lava with trapped gas bubbles: Dispersed Phase = Gas; Dispersion Medium = Solid. A gas dispersed in a solid medium is canonically classified as a "solid sol" (along with foam rubber). Instant 5-second answer!
1 Identify physical states in pumice stone: Gas trapped inside porous solid mineral.
2 Dispersed phase = Gas; Dispersion medium = Solid.
3 Refer to NCERT Table 5.4: Gas in Solid is classified as a "Solid sol".
4 Foam is Gas in Liquid; Gel is Liquid in Solid; Sol is Solid in Liquid.
5 Match Option (4) solid sol directly.
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Why You Can 100% Trust This Shortcut: Canonical NCERT Surface Chemistry classification of colloidal systems based on physical state of dispersed phase and dispersion medium.
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Physical Nature of Pumice Stone
Pumice stone is a highly vesicular, porous volcanic rock formed when gas bubbles remain trapped in rapidly cooling molten lava:
Step 2
Identify Dispersed Phase and Dispersion Medium
In pumice stone, the trapped gas bubbles constitute the dispersed phase, while the solid rock matrix constitutes the dispersion medium:
Step 3
Classify According to NCERT Colloidal Types
Referring to the standard eight colloidal classes based on physical states (Gas in Gas forms a true mixture):
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 (1)
✗ Incorrect Verdict & Scientific Reason:
Foam has liquid as dispersion medium and gas as dispersed phase (e.g., soap lather, whipped cream).
⚠️
Student Fallacy (Why candidates pick this trap): Candidate associated bubbly texture with foam, ignoring the solid dispersion medium.
2 (2)
✗ Incorrect Verdict & Scientific Reason:
Sol has solid dispersed in liquid medium (e.g., paints, cell fluids).
⚠️
Student Fallacy (Why candidates pick this trap): Candidate confused sol (solid in liquid) with solid sol.
3 (3)
✗ Incorrect Verdict & Scientific Reason:
Gel has liquid dispersed in solid medium (e.g., cheese, butter, jellies).
⚠️
Student Fallacy (Why candidates pick this trap): Candidate inverted the dispersed phase with liquid.
4 (4)
✓ 100% Correct Verdict & Scientific Reason:
Accurate: Gas dispersed in solid medium represents solid sol (e.g., pumice stone, foam rubber).
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Why this is airtight: None. Candidate correctly recalled the colloidal classification table.
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NTA Trap Alert: Confusing "Foam" with "Solid Sol"
Because pumice stone contains bubbly trapped gas, students often associate it with "foam". But "foam" strictly has a LIQUID dispersion medium. When the dispersion medium is SOLID, it is classified as a "solid sol"!
🛡️ How to avoid the -1 mark: Check dispersion medium: If medium is liquid → Foam; if medium is solid → Solid Sol.
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Core NEET Syllabus Standard
National Eligibility cum Entrance Test (NEET UG) · Surface Chemistry Standard Benchmark
Core Scientific Principle Tested:
"Colloidal systems are classified based on physical state: Gas dispersed in Solid is a solid sol."
Syllabus Focus: Classification of Colloids – Types of Colloidal Systems
Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗
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