Air University Entry Test Chemistry: Gases MCQs

Practice Gases MCQs for Air University Entry Test Chemistry — topic-wise sets with solved answers.

Air University Entry Test Chemistry: Gases MCQs — sample questions

  1. Question 1

    Q1. At constant temperature, the volume of a gas is inversely proportional to pressure. This is known as:

    • A) Charles' Law
    • B) Boyle's Law
    • C) Avogadro's Law
    • D) Graham's Law

    Answer: Boyle's Law

    Explanation: Boyle's Law states that P1V1 = P2V2 at constant temperature, showing inverse proportionality between volume and pressure.

  2. Question 2

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

    • A) Molecular mass
    • B) Density
    • C) Pressure
    • D) Temperature

    Answer: Molecular mass

    Explanation: Graham's Law states that rate of diffusion ∝ 1/√M, where M is molecular mass.

  3. Question 3

    Q3. The volume occupied by 1 mole of an ideal gas at STP is:

    • A) 11.2 L
    • B) 22.4 L
    • C) 33.6 L
    • D) 44.8 L

    Answer: 22.4 L

    Explanation: At STP, 1 mole of ideal gas occupies 22.4 L, as per Avogadro's hypothesis.

  4. Question 4

    Q4. The ratio of specific heats (Cp/Cv) for a diatomic gas is:

    • A) 1.33
    • B) 1.4
    • C) 1.67
    • D) 1.29

    Answer: 1.4

    Explanation: For diatomic gases, Cp/Cv = 7/5 = 1.4, due to 5 degrees of freedom.

  5. Question 5

    Q5. The pressure exerted by a mixture of non-reacting gases is the sum of their partial pressures. This is known as:

    • A) Dalton's Law
    • B) Henry's Law
    • C) Raoult's Law
    • D) Boyle's Law

    Answer: Dalton's Law

    Explanation: Dalton's Law states that P_total = P1 + P2 + ... for non-reacting gases.

  6. Question 6

    Q6. The temperature at which the volume of a gas becomes zero is:

    • A) 0°C
    • B) -273°C
    • C) 100°C
    • D) 273 K

    Answer: -273°C

    Explanation: At -273°C or 0 K, the volume of an ideal gas becomes zero, as per Charles' Law.

  7. Question 7

    Q7. The kinetic energy of 1 mole of an ideal gas is:

    • A) (3/2)RT
    • B) (5/2)RT
    • C) (3/2)PV
    • D) (5/2)PV

    Answer: (3/2)RT

    Explanation: Kinetic energy = (3/2)nRT, where n = 1 mole, so KE = (3/2)RT.

  8. Question 8

    Q8. The compressibility factor (Z) for an ideal gas is:

    • A) 0
    • B) 1
    • C) 2
    • D) -1

    Answer: 1

    Explanation: For ideal gases, PV = nRT, so Z = PV/nRT = 1.

  9. Question 9

    Q9. The van der Waals equation for 1 mole of a real gas is:

    • A) (P + a/V²)(V - b) = RT
    • B) (P - a/V²)(V + b) = RT
    • C) (P + a/V)(V - b) = RT
    • D) (P - a/V)(V + b) = RT

    Answer: (P + a/V²)(V - b) = RT

    Explanation: The van der Waals equation accounts for intermolecular forces (a) and molecular volume (b).

  10. Question 10

    Q10. The critical temperature (Tc) is the temperature above which a gas:

    • A) Cannot be liquefied
    • B) Can be liquefied
    • C) Behaves ideally
    • D) Diffuses rapidly

    Answer: Cannot be liquefied

    Explanation: Above Tc, the gas cannot be liquefied, no matter how high the pressure.

  11. Question 11

    Q11. The root mean square speed of gas molecules is proportional to:

    • A) √T
    • B) T
    • C) 1/√T
    • D) 1/T

    Answer: √T

    Explanation: The rms speed is given by √(3RT/M), so it is proportional to √T.

  12. Question 12

    Q12. The most probable speed of gas molecules is:

    • A) √(2RT/M)
    • B) √(3RT/M)
    • C) √(8RT/πM)
    • D) √(RT/M)

    Answer: √(2RT/M)

    Explanation: The most probable speed is given by √(2RT/M).

  13. Question 13

    Q13. The average kinetic energy of gas molecules is proportional to:

    • A) T
    • B) T²
    • C) 1/T
    • D) 1/T²

    Answer: T

    Explanation: The average KE is (3/2)kT, so it is directly proportional to T.

  14. Question 14

    Q14. The partial pressure of a gas in a mixture is 0.5 atm. If the total pressure is 2 atm, the mole fraction is:

    • A) 0.25
    • B) 0.5
    • C) 0.75
    • D) 1

    Answer: 0.25

    Explanation: Mole fraction = partial pressure / total pressure = 0.5/2 = 0.25.

  15. Question 15

    Q15. The density of a gas is 2 g/L at 1 atm and 27°C. The molecular mass is:

    • A) 24 g/mol
    • B) 48 g/mol
    • C) 49 g/mol
    • D) 50 g/mol

    Answer: 49 g/mol

    Explanation: Using PV = nRT and density = mass/volume, M = dRT/P = 2 * 0.0821 * 300 / 1 = 49.26 g/mol.

  16. Question 16

    Q16. The ratio of 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.

  17. Question 17

    Q17. The volume of a gas at 0°C and 1 atm is 100 mL. The volume at 273°C and 2 atm is:

    • A) 100 mL
    • B) 200 mL
    • C) 50 mL
    • D) 150 mL

    Answer: 50 mL

    Explanation: Using P1V1/T1 = P2V2/T2, we get V2 = P1V1T2 / P2T1 = (1 * 100 * 546) / (2 * 273) = 100 mL.

  18. Question 18

    Q18. The pressure of a gas is doubled at constant temperature. The volume becomes:

    • A) Double
    • B) Half
    • C) Unchanged
    • D) Quadruple

    Answer: Half

    Explanation: According to Boyle's Law, P1V1 = P2V2, so if P2 = 2P1, V2 = V1/2.

  19. Question 19

    Q19. The temperature of a gas is increased from 27°C to 127°C at constant pressure. The volume becomes:

    • A) 4/3 times
    • B) 3/4 times
    • C) 2 times
    • D) 1/2 times

    Answer: 4/3 times

    Explanation: Using Charles' Law, V1/T1 = V2/T2, so V2/V1 = T2/T1 = (400/300) = 4/3.

  20. Question 20

    Q20. The gas with the highest rate of diffusion is:

    • A) He
    • B) H2
    • C) O2
    • D) N2

    Answer: H2

    Explanation: H2 has the lowest molecular mass, so it diffuses the fastest according to Graham's Law.

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