Real and Ideal Gases

Real and Ideal Gases MDCAT MCQs with answers

9 past paper MCQs on Real and Ideal Gases, from the Gases unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.Real gases show deviation from ideal behaviour at: (MDCAT 2024)

  1. low temperature and low pressure
  2. high temperature and high pressure
  3. low temperature and high pressure
  4. high temperature and low pressure
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Correct answer: (c) low temperature and high pressure

Cold, compressed molecules are close together and slow, so their own volume and their attractions both matter.

2.Real gases show more positive deviation as pressure increases because of (SZABMU MDCAT 2025)

  1. Ionic nature
  2. repulsive forces
  3. attractive forces
  4. non polar nature
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Correct answer: (b) repulsive forces

Squeezed close, the molecules resist further compression, so the volume is larger than the ideal equation predicts.

3.Intermolecular forces between molecules of ideal gas are (UHS MDCAT 2024)

  1. Strong
  2. Moderate
  3. Weak
  4. Absent
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Correct answer: (d) Absent

An ideal gas is defined as one whose molecules neither attract nor repel each other.

4.The real gases show deviation from ideal behavior at: (UHS MDCAT 2024)

  1. Low temperature and low pressure
  2. High temperature and high pressure
  3. Low temperature and high pressure
  4. High temperature and low pressure
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Correct answer: (c) Low temperature and high pressure

Cooling and compressing bring the molecules close and slow, so their attractions begin to tell.

5.Intermolecular forces between gas molecules are significant at: (PMC MDCAT 2022)

  1. High temperature and low pressure
  2. Low temperature and high pressure
  3. At standard temperature and pressure
  4. At high temperature and high pressure
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Correct answer: (b) Low temperature and high pressure

Cooling and compressing bring the molecules close and slow, so their attractions begin to tell.

6.Which of the following postulate of kinetic molecular theory does NOT hold at high temperature and pressure? (PMC MDCAT 2022)

  1. Gases are considered to be composed of minute discrete particles called molecules.
  2. The molecules move in straight line.
  3. The pressure of gas is produced due to the collision of molecules with the wall of container.
  4. The volume occupied by the gas molecules is negligible as compared to the the total volume of the gas.
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Correct answer: (d) The volume occupied by the gas molecules is negligible as compared to the the total volume of the gas.

Squeezed close, the molecules take up a real fraction of the volume, and that is the assumption that fails.

7.Which one of the following is called as compressibility factor? (PMC MDCAT 2022)

  1. PV=nRT
  2. PV/nRT
  3. PV/RT=n
  4. PV/T=Rn
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Correct answer: (b) PV/nRT

$PV/nRT$ is the compressibility factor, one for an ideal gas and something else for a real one.

8.Gases behave ideally at: (PMC MDCAT 2022)

  1. under normal temperature and pressure conditions
  2. at room temperature and pressure
  3. at high temperature and low pressure
  4. at high pressure and low temperature
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Correct answer: (c) at high temperature and low pressure

Hot and thin, the molecules are far apart and moving fast, so their attractions and their own volume hardly count.

9.The actual volume of gas molecules is considered negligible at following pressures: (PMC MDCAT 2020)

  1. 2 atm
  2. 4 atm
  3. 6 atm
  4. 8 atm
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Correct answer: (a) 2 atm

The lower the pressure the further apart the molecules, so their own volume counts for least at $2\,\mathrm{atm}$.

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