NEET 2025 · PhysicsIdeal gasPrevious Year Question
An oxygen cylinder of volume 30 litre has 18.20 moles of oxygen. After some oxygen is withdrawn from the cylinder, its pressure drops to 11 atmospheric pressure at temperature 27 °C. The mass of the oxygen withdrawn from the cylinder is nearly equal to: [Given R = 100/12 J mol⁻¹ K⁻¹, molecular mass of O₂ = 32, 1 atm = 1.01 × 10⁵ N m⁻²]
Answer: (B) 0.156 kg. Correct Answer (B): 0.156 kg Apply PV = nRT to find the final number of moles n′ at the dropped pressure (11 atm), then subtract from the initial 18.20 moles to get the moles withdrawn, and convert to mass using the molar mass of O₂ (32 g mol⁻¹).
- A.0.116 kg
- B.0.156 kg✓
- C.0.125 kg
- D.0.144 kg
Correct Answer
(B) 0.156 kg
Solution & Explanation
Correct Answer (B): 0.156 kg Apply PV = nRT to find the final number of moles n′ at the dropped pressure (11 atm), then subtract from the initial 18.20 moles to get the moles withdrawn, and convert to mass using the molar mass of O₂ (32 g mol⁻¹). The unusual value R = 100/12 is chosen to make the arithmetic clean: n′ = PV/RT = 13.33 mol, so 4.87 mol (≈ 156 g) is withdrawn.
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