NEET Chemistry Questions & Answers

Q.1 Hard Physical Chemistry

For the reaction: A(g) + B(g) ⇌ C(g) + D(g), if initial pressures are PA = 2 atm, PB = 1 atm, and Kp = 4 at equilibrium PA = 0.5 atm, what is the equilibrium pressure of C?

A 1.5 atm

B 2.5 atm

C 3 atm

D 4 atm

Correct Answer: A. 1.5 atm

EXPLANATION

Initial: PA = 2, PB = 1. Change: -1.5 for A, -1.5 for B, +1.5 for C and D. Equilibrium: PA = 0.5, PB = -0.5 (invalid). Using Kp: 4 = (PC × PD)/(0.5 × PB). Since stoichiometry is 1:1:1:1, PC = PD = 1.5 atm.

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Q.2 Medium Physical Chemistry

Which of the following statements about chemical potential is correct?

A Chemical potential is always positive

B At equilibrium, chemical potentials of all phases are equal

C Chemical potential is independent of pressure

D Chemical potential is the same for all substances

Correct Answer: B. At equilibrium, chemical potentials of all phases are equal

EXPLANATION

At equilibrium, the chemical potential of a substance is the same in all phases present. This is the condition for phase equilibrium.

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Q.3 Hard Physical Chemistry

A first-order reaction is 75% complete in 45 minutes. What is the half-life of this reaction?

A 15 minutes

B 22.5 minutes

C 30 minutes

D 60 minutes

Correct Answer: B. 22.5 minutes

EXPLANATION

For first-order: ln([A]₀/[A]t) = kt. If 75% complete, [A]t = 0.25[A]₀. ln(4) = k × 45. Also, t₁/₂ = 0.693/k. From ln(4) = k × 45, k = ln(4)/45. t₁/₂ = 0.693 × 45/ln(4) ≈ 22.5 min.

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Q.4 Easy Physical Chemistry

In the Nernst equation at 25°C, what is the value of (2.303RT/F)?

A 0.026 V

B 0.059 V

C 0.0592 V

D 0.12 V

Correct Answer: C. 0.0592 V

EXPLANATION

At 25°C (298 K), (2.303RT/F) = (2.303 × 8.314 × 298)/96485 ≈ 0.0592 V. This is commonly used in half-cell potential calculations.

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Q.5 Hard Physical Chemistry

Which of the following has the lowest boiling point among hydrides of Group 16 elements?

A H₂O

B H₂S

C H₂Se

D H₂Te

Correct Answer: B. H₂S

EXPLANATION

Although H₂O has strong hydrogen bonding, the question asks for lowest. H₂S has the lowest boiling point (-60°C) among stable hydrides due to weak intermolecular forces. Note: H₂O has anomalously high bp due to H-bonding.

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Q.6 Medium Physical Chemistry

The osmotic pressure of a solution is 10 atm at 27°C. What is the molarity of the solution?

A 0.41 M

B 0.82 M

C 1.64 M

D 2.44 M

Correct Answer: A. 0.41 M

EXPLANATION

π = MRT, where π = 10 atm, T = 300 K, R = 0.0821 L·atm/(mol·K). M = π/(RT) = 10/(0.0821 × 300) ≈ 0.41 M.

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Q.7 Medium Physical Chemistry

A solution containing 0.5 mol of a non-volatile, non-electrolyte solute in 1 L of water shows a freezing point of -0.93°C. What is the cryoscopic constant (Kf) of water? (Tf of pure water = 0°C)

A 0.93 K·kg/mol

B 1.86 K·kg/mol

C 0.465 K·kg/mol

D 3.72 K·kg/mol

Correct Answer: B. 1.86 K·kg/mol

EXPLANATION

ΔTf = Kf × m, where m = molality = 0.5 mol/1 kg (approximately). ΔTf = 0.93°C, so Kf = 0.93/0.5 = 1.86 K·kg/mol.

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Q.8 Easy Physical Chemistry

Which colligative property is independent of the nature of the solute?

A Boiling point elevation

B Freezing point depression

C Osmotic pressure

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All colligative properties (boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering) depend only on the number of solute particles, not their nature.

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Q.9 Hard Physical Chemistry

If ΔG° = -40 kJ/mol at 298 K, what is the order of magnitude of the equilibrium constant K?

A K < 1

B K = 1

C K >> 1 (very large)

D K ≈ 10⁻¹

Correct Answer: C. K >> 1 (very large)

EXPLANATION

ΔG° = -RT ln K. With ΔG° = -40 kJ/mol = -40000 J/mol, ln K = 40000/(8.314 × 298) ≈ 16.2, so K = e^16.2 >> 1 (very large).

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Q.10 Medium Physical Chemistry

The cell potential (E°cell) for a reaction is -0.5 V. Which statement is correct?

A The reaction is spontaneous under standard conditions

B The reaction is non-spontaneous under standard conditions

C ΔG° = +RT ln K

D Kequilibrium < 1

Correct Answer: B. The reaction is non-spontaneous under standard conditions

EXPLANATION

When E°cell is negative, ΔG° = -nFE°cell is positive, making the reaction non-spontaneous. Also, negative E°cell indicates Kequilibrium < 1.

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