Q122 / 180 · COMEDK 2026 (9 May Shift 2) · Physics
A vessel of volume $27 \times 10^4$ cc, contains a mixture of Hydrogen (molar mass $= 2\ g\ mol^{-1}$) and oxygen (molar mass $= 32\ g\ mol^{-1}$) gas at standard temperature and pressure. If the mass of hydrogen is 16 g, find the mass of oxygen gas contained in the vessel.
- A$72$ g
- Correct answerB$129.7$ g
- C$64$ g
- D$160$ g
Solution
Volume of the vessel, $V = 27 \times 10^4$ cc $= 270$ L
At STP, the volume of $1$ mole of an ideal gas is $22.4$ L.
Total number of moles in the mixture, $n = \dfrac{270}{22.4} \approx 12.054$
Number of moles of hydrogen, $n_{H_2} = \dfrac{16}{2} = 8$
Number of moles of oxygen, $n_{O_2} = n - n_{H_2} = 12.054 - 8 = 4.054$
Mass of oxygen, $m_{O_2} = n_{O_2} \times 32 = 4.054 \times 32 \approx 129.7$ g
Answer: $129.7$ g
At STP, the volume of $1$ mole of an ideal gas is $22.4$ L.
Total number of moles in the mixture, $n = \dfrac{270}{22.4} \approx 12.054$
Number of moles of hydrogen, $n_{H_2} = \dfrac{16}{2} = 8$
Number of moles of oxygen, $n_{O_2} = n - n_{H_2} = 12.054 - 8 = 4.054$
Mass of oxygen, $m_{O_2} = n_{O_2} \times 32 = 4.054 \times 32 \approx 129.7$ g
Answer: $129.7$ g
Hence, the correct answer is option: 'B'.