67 past paper MCQs from Chemistry unit 3, Gases, across 8 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.
1.The process of heat flow between hotter and colder gases continues until all the molecules have equal: (MDCAT 2022)
Correct answer: (a) average translational kinetic energy
Temperature measures the average translational kinetic energy, and heat flows until the two gases share it equally.
2.The process of heat flow between hotter and colder bodies stops when their molecules have equal: (MDCAT 2023)
Correct answer: (a) average translational kinetic energy
Temperature is a measure of the average translational kinetic energy, and heat flows until the two are equal.
3.The intermolecular forces between the molecules of an ideal gas are: (MDCAT 2024)
Correct answer: (d) absent
The kinetic theory of an ideal gas assumes no attraction between the molecules at all.
All 19 Kinetic Molecular Theory MCQs → Kinetic Molecular Theory notes →
4.Half of atmospheric pressure is: (MDCAT 2020)
Correct answer: (b) 50662 Pa
One atmosphere is 101325 Pa, so half of it is 50662 Pa.
5.Consider the equation H2 + O2 -> H2O, what volume of hydrogen gas is required to produce 1 mol of water at standard temperature & pressure? (UHS MDCAT 2025)
Correct answer: (b) 22.4 dm3
One mole of water needs one mole of hydrogen, and a mole of any gas fills $22.4\,\mathrm{dm^3}$ at STP.
6.Select the standard condition for temperature and pressure: (SIBA MDCAT 2025)
Correct answer: (d) 14.7 psi and 0°C
Standard conditions are one atmosphere, that is $14.7\,\mathrm{psi}$, and $0^{\circ}\mathrm{C}$.
All 7 Standard Temperature and Pressure MCQs → Standard Temperature and Pressure notes →
7.At constant pressure, at which temperature will the volume of a gas become twice its volume at $0^\circ$C? (MDCAT 2020)
Correct answer: (c) $273^\circ$C
Volume goes as the absolute temperature, so it doubles when 273 K becomes 546 K, which is $273^\circ$C.
8.A gas has volume 10dm3 at 10°C. At what temperature is volume reduced to half? (NUMS MDCAT 2024)
Correct answer: (c) 142K
At constant pressure the volume follows the absolute temperature, so halving it halves $283\,\mathrm{K}$ to about $142\,\mathrm{K}$.
9.According to Charles law volume of gas reduces to zero at: (SZABMU MDCAT 2023)
Correct answer: (c) -273.15 O C
Extrapolating the volume line to zero gives $-273.15^{\circ}\mathrm{C}$.
All 5 Charles's Law MCQs → Charles's Law notes →
10.The product of volume and pressure of fixed amount of a gas at constant temperature remains same for initial and final state of a gaseous system. This statement corresponds to: (PMC MDCAT 2022)
Correct answer: (c) Boyle's law
That is Boyle’s law.
11.A graph between volume and temperature gives a straight line which cuts the temperature axis at: (MDCAT 2020)
Correct answer: (b) $-273^\circ$C
Extrapolated to zero volume the line meets the axis at absolute zero, $-273^\circ$C.
12.The starting point of the Kelvin scale is: (MDCAT 2020)
Correct answer: (a) 0 K
The Kelvin scale begins at absolute zero, which is 0 K by definition.
13.Which of the following is true about pressure for an ideal gas at -273°C? (UHS MDCAT 2025)
Correct answer: (d) P=0 atm
At absolute zero the molecular motion stops, so the gas would exert no pressure at all.
All 5 Absolute Zero MCQs → Absolute Zero notes →
14.The expression $PV=nRT$ represents the: (MDCAT 2020)
Correct answer: (c) general gas equation
It is the ideal or general gas equation, got by combining the laws of Boyle, Charles and Avogadro.
15.The correct ideal gas equation is: (MDCAT 2024)
Correct answer: (b) $PV=nRT$
$PV=nRT$, with $T$ the absolute temperature.
16.When pressure is 1520 torr then density of oxygen gas will be: (SIBA MDCAT 2025)
Correct answer: (a) 64/RT
$1520\,\mathrm{torr}$ is two atmospheres, and $d=PM/RT$ gives $2\times32/RT$.
All 15 Ideal Gas Equation MCQs → Ideal Gas Equation notes →
17.If we want to raise the temperature of one mole of an ideal gas by one kelvin, how much energy do we have to provide? (MDCAT 2022)
Correct answer: (d) $0.0821\ \mathrm{dm^3\,atm}$
That energy is the gas constant itself, $R=8.314\ \mathrm{J\,mol^{-1}K^{-1}}=0.0821\ \mathrm{dm^3\,atm\,mol^{-1}K^{-1}}$.
18.Value of R gas constant in J mol-1 K-1 is (UHS MDCAT 2025)
Correct answer: (a) 8.314
In SI units the gas constant is $8.314\,\mathrm{J\,mol^{-1}\,K^{-1}}$.
19.The value of R in atm.dm3.mol-1.K-1 is: (KMU MDCAT 2025)
Correct answer: (a) 0.0821
In these units the gas constant is $0.0821\,\mathrm{atm\,dm^3\,mol^{-1}\,K^{-1}}$.
All 6 The Gas Constant R MCQs → The Gas Constant R notes →
20.Real gases show deviation from ideal behaviour at: (MDCAT 2024)
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.
21.Real gases show more positive deviation as pressure increases because of (SZABMU MDCAT 2025)
Correct answer: (b) repulsive forces
Squeezed close, the molecules resist further compression, so the volume is larger than the ideal equation predicts.
22.Intermolecular forces between molecules of ideal gas are (UHS MDCAT 2024)
Correct answer: (d) Absent
An ideal gas is defined as one whose molecules neither attract nor repel each other.
All 9 Real and Ideal Gases MCQs → Real and Ideal Gases notes →