Riphah International University Medical Entry Chemistry: Gases MCQs

Riphah International University Medical Entry Chemistry: Gases MCQs — sample questions

1. Question 1

   Q1. At standard temperature and pressure, the molar volume of an ideal gas is

   • A) 20.0 dm³
   • B) 22.4 dm³
   • C) 24.0 dm³
   • D) 25.4 dm³

   Answer: 22.4 dm³

   Explanation: Molar volume at STP is 22.4 dm³; option B is correct. Option D is at 25°C and 1 atm.

2. Question 2

   Q2. The rate of diffusion of a gas is inversely proportional to the square root of its

   • A) density
   • B) molecular mass
   • C) pressure
   • D) temperature

   Answer: molecular mass

   Explanation: Graham's law states rate ∝ 1/√M; molecular mass is correct. Density is related but not directly used.

3. Question 3

   Q3. A real gas behaves most like an ideal gas at

   • A) high pressure and low temperature
   • B) low pressure and high temperature
   • C) high pressure and high temperature
   • D) low pressure and low temperature

   Answer: low pressure and high temperature

   Explanation: Low pressure and high temperature minimize intermolecular forces, making a real gas behave like an ideal gas.

4. Question 4

   Q4. The partial pressure of a gas in a mixture is

   • A) the pressure exerted by the gas if it alone occupied the total volume
   • B) the total pressure divided by the number of gases
   • C) the pressure exerted by the gas at absolute zero
   • D) the total pressure minus the vapor pressure of other components

   Answer: the pressure exerted by the gas if it alone occupied the total volume

   Explanation: Partial pressure is the pressure a gas would exert if it alone occupied the total volume; Dalton's Law.

5. Question 5

   Q5. The kinetic molecular theory assumes that gas molecules

   • A) have significant intermolecular forces
   • B) occupy a significant fraction of the total volume
   • C) are in constant random motion
   • D) have varying kinetic energies at a given temperature

   Answer: are in constant random motion

   Explanation: Kinetic theory assumes gas molecules are in constant random motion; option C is correct. Option D is incorrect because kinetic energy is directly related to temperature.

6. Question 6

   Q6. The critical temperature of a gas is the temperature

   • A) above which it cannot be liquefied
   • B) below which it cannot be liquefied
   • C) at which its vapor pressure is maximum
   • D) at which its density is maximum

   Answer: above which it cannot be liquefied

   Explanation: Critical temperature is the maximum temperature at which a gas can be liquefied; above it, liquefaction is impossible.

7. Question 7

   Q7. A gas deviates from ideal behavior because its molecules

   • A) have kinetic energy
   • B) are in constant motion
   • C) have intermolecular forces
   • D) collide elastically

   Answer: have intermolecular forces

   Explanation: Real gases deviate from ideal behavior due to intermolecular forces; option C is correct. Options A, B, and D are assumptions of ideal gas behavior.

8. Question 8

   Q8. The vapor pressure of a liquid is the pressure exerted by the vapor

   • A) when the rate of evaporation equals the rate of condensation
   • B) when the liquid is at its boiling point
   • C) at absolute zero
   • D) in a vacuum

   Answer: when the rate of evaporation equals the rate of condensation

   Explanation: Vapor pressure is the pressure exerted when evaporation and condensation rates are equal; equilibrium condition.

9. Question 9

   Q9. The boiling point of a liquid is the temperature at which its vapor pressure

   • A) equals the atmospheric pressure
   • B) is less than the atmospheric pressure
   • C) is greater than the atmospheric pressure
   • D) equals the critical pressure

   Answer: equals the atmospheric pressure

   Explanation: Boiling occurs when vapor pressure equals atmospheric pressure; option A is correct.

10. Question 10

    Q10. At constant temperature, the volume of a given mass of an ideal gas is

    • A) directly proportional to its pressure
    • B) inversely proportional to its pressure
    • C) directly proportional to the square of its pressure
    • D) inversely proportional to the square of its pressure

    Answer: inversely proportional to its pressure

    Explanation: Boyle's Law states V ∝ 1/P at constant T; option B is correct.

11. Question 11

    Q11. The density of a gas is directly proportional to its

    • A) molecular mass
    • B) temperature
    • C) pressure
    • D) volume

    Answer: molecular mass

    Explanation: Density = mass/volume; for a given volume, density ∝ molecular mass at constant T and P.

12. Question 12

    Q12. The effusion rate of a gas through a small orifice is inversely proportional to the square root of its

    • A) density
    • B) molecular mass
    • C) pressure
    • D) temperature

    Answer: molecular mass

    Explanation: Graham's law applies to effusion; rate ∝ 1/√M, so molecular mass is correct.

13. Question 13

    Q13. A mixture of gases can be separated by

    • A) diffusion through a porous barrier
    • B) adsorption on activated charcoal
    • C) fractional distillation
    • D) all the above methods

    Answer: all the above methods

    Explanation: Gases can be separated by diffusion (Graham's law), adsorption, or fractional distillation; all are valid methods.

14. Question 14

    Q14. The pressure exerted by a gas is due to

    • A) the intermolecular forces between its molecules
    • B) the collisions of its molecules with the container walls
    • C) the gravitational attraction between its molecules
    • D) the volume occupied by its molecules

    Answer: the collisions of its molecules with the container walls

    Explanation: Pressure is due to collisions of gas molecules with container walls; kinetic molecular theory.

15. Question 15

    Q15. The absolute zero on the Celsius scale is

    • A) -273.15°C
    • B) 0°C
    • C) -100°C
    • D) 100°C

    Answer: -273.15°C

    Explanation: Absolute zero is 0 K, which is -273.15°C; option A is correct.

16. Question 16

    Q16. A real gas behaves like an ideal gas at

    • A) low temperature and high pressure
    • B) high temperature and low pressure
    • C) high temperature and high pressure
    • D) low temperature and low pressure

    Answer: high temperature and low pressure

    Explanation: High temperature and low pressure minimize intermolecular forces, making real gases behave ideally.

17. Question 17

    Q17. The ratio of the rates of diffusion of two gases is 2:1. The ratio of their molecular masses is

    • A) 1:4
    • B) 4:1
    • C) 1:2
    • D) 2:1

    Answer: 1:4

    Explanation: According to Graham's law, rate ∝ 1/√M; so M1/M2 = (rate2/rate1)² = (1/2)² = 1/4.

18. Question 18

    Q18. The temperature at which the vapor pressure of a liquid equals the external pressure is its

    • A) boiling point
    • B) melting point
    • C) critical temperature
    • D) triple point

    Answer: boiling point

    Explanation: Boiling point is defined as the temperature where vapor pressure equals external pressure; option A is correct.

19. Question 19

    Q19. The van der Waals equation corrects the ideal gas law for

    • A) the volume occupied by gas molecules and intermolecular forces
    • B) the pressure and temperature of the gas
    • C) the number of moles of gas
    • D) the gas constant

    Answer: the volume occupied by gas molecules and intermolecular forces

    Explanation: Van der Waals equation corrects for molecular volume (b) and intermolecular forces (a); option A is correct.

20. Question 20

    Q20. The average kinetic energy of gas molecules is directly proportional to the

    • A) pressure of the gas
    • B) volume of the gas
    • C) temperature of the gas
    • D) number of moles of gas

    Answer: temperature of the gas

    Explanation: Kinetic energy is directly proportional to temperature; from kinetic molecular theory, KE ∝ T.