Q.77 Chemistry · Section A ⭐ 360° Option Elimination Active

NEET 2024 Chemistry Question 77 Solution

Topic: Solutions · Official NTA Booklet Code T1

Question

The Henry's law constant (K_H) values of three gases (A, B, C) in water are 145, 2×10⁻⁵ and 35 kbar, respectively. The solubility of these gases in water follow the order:

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Verified Against NTA Final Answer Key

Option (4) : B > C > A

📚 Solutions Easy

📋 Given Parameters & Problem Setup

Henry’s constant for Gas A (K_H,A) 145 kbar

Henry’s constant for Gas B (K_H,B) 2 × 10^-5 kbar

Henry’s constant for Gas C (K_H,C) 35 kbar

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The 30-Second Exam Hall Shortcut: ⚡ Inverse Henry Constant Rule

⏱️ Save ~30 seconds

Solubility x ∝ (1 / K_H)! Lowest K_H means HIGHEST solubility! K_H order: B (2e-5) < C (35) < A (145) -> Solubility: B > C > A!

1 Henry’s Law: p = K_H · x, where x is mole fraction solubility.

2 Rearranging gives: x = p / K_H.

3 At a constant partial pressure, gas solubility is INVERSELY proportional to Henry’s constant K_H.

4 Order of K_H: K_H(B) [2 × 10⁻⁵ kbar] < K_H(C) [35 kbar] < K_H(A) [145 kbar].

5 Therefore, solubility order is exactly inverted: B > C > A.

6 Match Option (4) in 5 seconds!

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Why You Can 100% Trust This Shortcut: NCERT Chemistry · Solutions (Henry’s law: higher the value of KH at a given pressure, the lower is the solubility of the gas in the liquid).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Henry’s Law Mathematical Relationship

Henry’s law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution:

p = K_H \cdot x \implies x = \frac{p}{K_H}

Step 2

Inverse Proportionality Between Solubility and KH

From the rearranged equation, at a given constant pressure p, the mole fraction x (which measures gas solubility) is inversely proportional to the Henry’s law constant KH: Higher KH -> Lower solubility Lower KH -> Higher solubility

x \propto \frac{1}{K_H} \quad (\text{at constant } p)

Step 3

Ordering the Gases by Given KH Values

Listing the given KH values in increasing numerical order: - Gas B: KH = 2 × 10⁻⁵ kbar (exceptionally small KH -> maximum solubility) - Gas C: KH = 35 kbar (intermediate KH -> moderate solubility) - Gas A: KH = 145 kbar (largest KH -> minimum solubility)

K_H(B) \;[2\times 10^{-5}] < K_H(C) \;[35] < K_H(A) \;[145] \implies x_B > x_C > x_A

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 (1)

✗ Incorrect

Verdict & Scientific Reason:

Assumes direct proportionality between solubility and KH (order of KH values, not solubility).

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Student Fallacy (Why candidates pick this trap): Thinking higher KH means higher solubility.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Completely incorrect ordering of KH values.

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Student Fallacy (Why candidates pick this trap): Misreading exponents.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Places A above C in solubility even though KH(A) > KH(C).

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Student Fallacy (Why candidates pick this trap): Partial inversion.

4 (4)

✓ 100% Correct

Verdict & Scientific Reason:

Exact inverse ordering of Henry’s law constants: B (lowest KH) > C > A (highest KH).

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Why this is airtight: None.

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NTA Trap Alert: Option (1) Direct Proportionality Trap

Students frequently treat KH like an equilibrium solubility constant (Ksp) where bigger means more soluble. For Henry’s constant, BIGGER KH MEANS LESS SOLUBLE!

🛡️ How to avoid the -1 mark: Recite the verbatim NCERT phrase: "Higher the value of KH at a given pressure, lower is the solubility of the gas."

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Core NEET Syllabus Standard

Chemistry Core Physical Chemistry · Solutions Standard Benchmark

Core Scientific Principle Tested:

"Solubility of a gas is inversely proportional to its Henry’s law constant KH at constant pressure: x = p / KH."

Syllabus Focus: Solubility of Gases in Liquids: Henry’s Law Constant

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

High KH means gas hates the drink: Low KH lets it dissolve in a wink (B > C > A)!

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NEET 2024 Chemistry Question 77 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Inverse Henry Constant Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Henry’s Law Mathematical Relationship

Inverse Proportionality Between Solubility and KH

Ordering the Gases by Given KH Values

360° Option Elimination Engine Key Feature

NTA Trap Alert: Option (1) Direct Proportionality Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Solutions

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