Gases MCQs With Answer offers B. Pharm students a focused, exam-oriented review of gaseous behavior relevant to pharmaceutical sciences. This concise introduction covers core concepts such as ideal and real gas laws, partial pressures, diffusion and effusion, kinetic molecular theory, gas sterilization, inhalation therapies, and analytical techniques like gas chromatography. Each question emphasizes clinical and formulation relevance, helping you link theory to practice in drug storage, delivery and safety. Keywords included: Gases MCQs With Answer, gas laws, van der Waals, partial pressure, diffusion, sterilization, inhalation therapy, gas chromatography, B. Pharm. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What does the ideal gas law PV = nRT assume about gas molecules?
- They have significant volume and strong intermolecular forces
- They occupy no volume and exert no intermolecular forces
- They are always in chemical equilibrium with the surroundings
- They react with container walls to maintain pressure
Correct Answer: They occupy no volume and exert no intermolecular forces
Q2. Which law relates partial pressures of gases to the total pressure of a mixture?
- Boyle’s law
- Charles’s law
- Dalton’s law
- Graham’s law
Correct Answer: Dalton’s law
Q3. According to Graham’s law, the rate of effusion of a gas is inversely proportional to what property?
- Temperature
- Molar mass (square root)
- Pressure
- Volume
Correct Answer: Molar mass (square root)
Q4. The van der Waals equation corrects the ideal gas law by accounting for:
- Electrical conductivity of gases
- Intermolecular attractions and finite molecular volume
- Radioactive decay of gas molecules
- Gas solubility in water
Correct Answer: Intermolecular attractions and finite molecular volume
Q5. The compressibility factor Z = PV/RT indicates what about a gas?
- Whether the gas obeys Avogadro’s law exactly
- Degree of deviation from ideal gas behavior
- The solubility of gas in organic solvents
- Specific heat capacity at constant volume
Correct Answer: Degree of deviation from ideal gas behavior
Q6. Which effect describes temperature change of a gas when it expands through a porous plug or valve at constant enthalpy?
- Charles effect
- Joule-Thomson effect
- Boiling point elevation
- Boyle inversion
Correct Answer: Joule-Thomson effect
Q7. Henry’s law is most relevant to which pharmaceutical concept?
- Drug partitioning in solid dispersions
- Gas solubility in blood and fluids
- Covalent drug binding to proteins
- Evaporation of solvents from creams
Correct Answer: Gas solubility in blood and fluids
Q8. The Maxwell–Boltzmann distribution describes:
- Distribution of molecular speeds in a gas sample
- pH distribution in buffer systems
- Concentration gradients across membranes
- Particle size distribution in suspensions
Correct Answer: Distribution of molecular speeds in a gas sample
Q9. Which gas is commonly used for sterilization of heat-sensitive pharmaceutical equipment?
- Nitrous oxide
- Ethylene oxide
- Carbon monoxide
- Hydrogen
Correct Answer: Ethylene oxide
Q10. In gas chromatography, which property of the carrier gas is most critical?
- It must be the heaviest gas available
- It must be inert and have appropriate flow characteristics
- It must be reactive to help separate analytes
- It must be highly polar
Correct Answer: It must be inert and have appropriate flow characteristics
Q11. Which parameter decreases when a real gas is cooled at constant pressure near its condensation point?
- Intermolecular attractions
- Deviation from ideal behavior
- Molecular mass
- Partial pressure of inert gases
Correct Answer: Deviation from ideal behavior
Q12. Root mean square speed of gas molecules depends on which of the following?
- Molar mass and temperature
- Volume and pressure only
- Number of moles only
- Intermolecular forces only
Correct Answer: Molar mass and temperature
Q13. Dalton’s law is essential in respiratory therapy because it helps calculate:
- Gas viscosity in ventilators
- Partial pressure of oxygen in inspired air
- Blood viscosity changes
- Drug degradation rates
Correct Answer: Partial pressure of oxygen in inspired air
Q14. Which gas is a common inhalation anesthetic and has analgesic properties?
- Oxygen
- Nitrous oxide
- Carbon dioxide
- Helium
Correct Answer: Nitrous oxide
Q15. The Virial equation of state provides corrections to ideal gas behavior using:
- Series expansion in powers of number density
- Chemical reaction rates
- Viscosity coefficients only
- pH-dependent terms
Correct Answer: Series expansion in powers of number density
Q16. Which statement about effusion is correct?
- Heavier gases effuse faster than lighter gases
- Effusion rate is independent of molecular mass
- Lighter gases effuse faster than heavier gases
- Effusion only occurs in liquids
Correct Answer: Lighter gases effuse faster than heavier gases
Q17. Which of the following influences the vapor pressure of a volatile drug?
- Molecular structure and temperature
- Only the color of the drug
- Ambient magnetic field
- Number of tablets in a bottle
Correct Answer: Molecular structure and temperature
Q18. In pharmaceutical packaging, why is knowledge of gas permeability important?
- It determines the tablet dissolution rate directly
- It affects drug stability by controlling moisture and oxygen ingress
- It changes drug molecular weight
- It alters active ingredient potency chemically
Correct Answer: It affects drug stability by controlling moisture and oxygen ingress
Q19. Which gas property is most relevant when calculating oxygen therapy dosing using partial pressure?
- Viscosity
- Partial pressure of oxygen
- Diffusivity of inert gases
- Molecular polarity
Correct Answer: Partial pressure of oxygen
Q20. The Clausius–Clapeyron equation relates which two quantities?
- Viscosity and density
- Enthalpy of vaporization and vapor pressure with temperature
- Diffusion coefficient and membrane thickness
- pKa and pH
Correct Answer: Enthalpy of vaporization and vapor pressure with temperature
Q21. A real gas shows Z < 1 at certain conditions. This implies:
- Repulsive forces dominate
- Attractive forces dominate
- Gas is ideal
- Molecular mass is zero
Correct Answer: Attractive forces dominate
Q22. Which gas analysis technique separates components based on volatility and interaction with a stationary phase?
- High-performance liquid chromatography
- Gas chromatography
- Mass spectrometry without separation
- UV-visible spectroscopy
Correct Answer: Gas chromatography
Q23. What is the significance of critical temperature for a substance?
- Below this temperature, the substance cannot be liquefied by pressure alone
- It is the temperature at which solids sublimate directly to gas
- It is the highest temperature at which gas reacts with water
- It is the boiling point at 0.5 atm
Correct Answer: Below this temperature, the substance cannot be liquefied by pressure alone
Q24. What does mean free path refer to in gas kinetics?
- Average distance between container walls
- Average distance a molecule travels between collisions
- Total path length in chromatography
- Distance required for complete diffusion across membranes
Correct Answer: Average distance a molecule travels between collisions
Q25. In drug inhalation, the rate of gas exchange in alveoli is most affected by:
- Surface area and partial pressure gradients
- Tablet disintegration time
- Oral bioavailability
- Drug taste
Correct Answer: Surface area and partial pressure gradients
Q26. Which of the following gases is most soluble in blood at body temperature?
- Nitrogen
- Oxygen
- Carbon dioxide
- Helium
Correct Answer: Carbon dioxide
Q27. For an ideal gas, doubling the temperature (Kelvin) at constant volume results in:
- Half the pressure
- No change in pressure
- Doubling of pressure
- Fourfold increase in pressure
Correct Answer: Doubling of pressure
Q28. Which gas is most commonly used as an inert blanket to reduce oxidation in pharmaceutical packaging?
- Oxygen
- Nitrogen
- Carbon monoxide
- Hydrogen sulfide
Correct Answer: Nitrogen
Q29. The kinetic molecular theory predicts that at the same temperature, which gas has the highest average molecular speed?
- Gas with highest molar mass
- Gas with lowest molar mass
- All gases have same speed regardless of mass
- Gas with highest density
Correct Answer: Gas with lowest molar mass
Q30. Which law explains the inverse relationship between pressure and volume at constant temperature?
- Charles’s law
- Boyle’s law
- Avogadro’s law
- Henry’s law
Correct Answer: Boyle’s law
Q31. When storing pressurized medical oxygen cylinders, which property of gases must be considered?
- Chemical reactivity with polyethylene only
- High compressibility and pressure safety limits
- Color of the cylinder only
- Solubility in ethanol
Correct Answer: High compressibility and pressure safety limits
Q32. Which factor does NOT affect the rate of gas diffusion through a membrane?
- Concentration gradient
- Membrane surface area
- Molar mass of the diffusing gas
- Color of the membrane
Correct Answer: Color of the membrane
Q33. In a gas mixture, if the mole fraction of gas A is 0.2 and total pressure is 1 atm, the partial pressure of A is:
- 0.2 atm
- 5 atm
- 1.2 atm
- 0.02 atm
Correct Answer: 0.2 atm
Q34. Which gas is toxic and binds strongly to hemoglobin, preventing oxygen transport?
- Nitrogen
- Carbon monoxide
- Carbon dioxide
- Helium
Correct Answer: Carbon monoxide
Q35. The molar volume of an ideal gas at STP (0°C, 1 atm) is approximately:
- 22.4 L/mol
- 1.0 L/mol
- 0.082 L/mol
- 44.8 L/mol
Correct Answer: 22.4 L/mol
Q36. Which phenomenon explains why inhaled anesthetic uptake depends on blood/gas partition coefficient?
- Partitioning between blood and gas phases affects arterial concentration and onset
- Color change of the anesthetic
- Solid-state diffusion
- Evaporation into the atmosphere
Correct Answer: Partitioning between blood and gas phases affects arterial concentration and onset
Q37. What does the term “partial pressure” in Henry’s law determine for a gas dissolved in liquid?
- The chemical reactivity in solids
- Equilibrium concentration of the gas in the liquid
- Color intensity of the solution
- Rate of solid dissolution
Correct Answer: Equilibrium concentration of the gas in the liquid
Q38. Which gas is commonly used as a tracer in pulmonary function testing due to its low solubility?
- Helium
- Carbon dioxide
- Nitric oxide
- Oxygen
Correct Answer: Helium
Q39. In the van der Waals equation, the constant ‘a’ accounts for:
- Molecular shape only
- Attractive forces between molecules
- Finite molecular volume
- Temperature dependence of pressure
Correct Answer: Attractive forces between molecules
Q40. Which of the following is a correct unit conversion for pressure?
- 1 atm = 760 mm Hg
- 1 atm = 7600 mm Hg
- 1 atm = 101.3 mm Hg
- 1 atm = 14,700 mm Hg
Correct Answer: 1 atm = 760 mm Hg
Q41. The rate of effusion of hydrogen gas compared to oxygen is approximately:
- Slower because hydrogen is heavier
- Faster because hydrogen has lower molar mass
- The same because mass does not matter
- Zero because hydrogen does not effuse
Correct Answer: Faster because hydrogen has lower molar mass
Q42. Which gas property is directly proportional to the absolute temperature for an ideal gas at constant pressure?
- Volume
- Mass
- Number of particles
- Intermolecular attraction
Correct Answer: Volume
Q43. In pharmacology, why is CO2 retention dangerous in patients under anesthesia?
- CO2 is inert and has no physiological effects
- Hypercapnia leads to respiratory acidosis and cardiovascular effects
- CO2 binds hemoglobin and increases oxygen delivery
- CO2 decreases blood pressure by acting as a vasodilator only
Correct Answer: Hypercapnia leads to respiratory acidosis and cardiovascular effects
Q44. What happens to gas solubility in liquids as temperature increases (generally)?
- Solubility increases for most gases
- Solubility decreases for most gases
- Temperature has no effect
- Solubility becomes infinite
Correct Answer: Solubility decreases for most gases
Q45. Which term describes the pressure exerted by water vapor in a closed container at equilibrium?
- Vapor pressure
- Osmotic pressure
- Hydrostatic pressure
- Vapor density
Correct Answer: Vapor pressure
Q46. In kinetic theory, pressure of a gas results from:
- Chemical bonds breaking
- Collisions of molecules with container walls
- Electrostatic attraction between molecules
- Gravitational pull of gas molecules
Correct Answer: Collisions of molecules with container walls
Q47. Which gas is commonly used to reduce work of breathing due to its low density when mixed with oxygen?
- Carbon dioxide
- Helium
- Nitrogen dioxide
- Sulfur dioxide
Correct Answer: Helium
Q48. If 2 moles of an ideal gas occupy 11.2 L at STP, how many liters would 1 mole occupy at STP?
- 5.6 L
- 22.4 L
- 11.2 L
- 2.24 L
Correct Answer: 11.2 L
Q49. Which gas is primarily responsible for the greenhouse effect but is also a normal metabolic product in humans?
- Oxygen
- Carbon dioxide
- Nitrogen
- Argon
Correct Answer: Carbon dioxide
Q50. When using the ideal gas law in pharmaceutical calculations, which unit set is consistent with R = 0.08206 L·atm·K⁻¹·mol⁻¹?
- Pressure in kPa, volume in mL, temperature in °C
- Pressure in atm, volume in L, temperature in K
- Pressure in atm, volume in m³, temperature in °C
- Any units are acceptable without conversion
Correct Answer: Pressure in atm, volume in L, temperature in K
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