Gaseous methods of sterilization MCQs With Answer is a focused, SEO-friendly resource tailored for B. Pharm students studying sterilization in pharmacy practice. This concise introduction and question set covers gaseous sterilization techniques — ethylene oxide (EO), vaporized hydrogen peroxide (VHP), ozone, formaldehyde and plasma sterilization — and explains mechanisms, critical parameters (temperature, humidity, exposure time), material compatibility, safety, biological and chemical indicators, sterilization validation (D-value, SAL) and monitoring. Each multiple-choice question reinforces deeper understanding of sterilant chemistry, equipment selection, process control and regulatory standards relevant to pharmaceutical and medical device sterilization. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which gaseous sterilant inactivates microorganisms primarily by alkylation of nucleic acids and proteins?
- Vaporized hydrogen peroxide
- Ethylene oxide
- Ozone
- Formaldehyde
Correct Answer: Ethylene oxide
Q2. What is the primary mechanism of action for vaporized hydrogen peroxide (VHP) sterilization?
- Alkylation of nucleic acids
- Oxidation by free radicals
- Cross-linking of proteins
- Hydrolysis of cell walls
Correct Answer: Oxidation by free radicals
Q3. Which biological indicator organism is commonly used to validate ethylene oxide sterilization?
- Geobacillus stearothermophilus
- Bacillus atrophaeus
- Clostridium botulinum
- Staphylococcus aureus
Correct Answer: Bacillus atrophaeus
Q4. Why is aeration an essential post-process step after ethylene oxide sterilization?
- To cool the load
- To remove toxic EO residues and by-products
- To increase sterilant concentration
- To dry the load completely
Correct Answer: To remove toxic EO residues and by-products
Q5. Which gaseous sterilant decomposes into water and oxygen, leaving minimal toxic residues?
- Ethylene oxide
- Vaporized hydrogen peroxide
- Formaldehyde
- Chlorine dioxide
Correct Answer: Vaporized hydrogen peroxide
Q6. Gas plasma sterilization (low-temperature plasma) inactivates microorganisms mainly by which mechanism?
- Thermal denaturation
- Reactive species and UV-generated damage
- Alkylation of DNA
- Desiccation
Correct Answer: Reactive species and UV-generated damage
Q7. Which gaseous sterilant is a strong oxidizing agent commonly used for surface and environmental decontamination and requires controlled humidity?
- Ethylene oxide
- Ozone
- Carbon dioxide
- Nitrogen
Correct Answer: Ozone
Q8. Formaldehyde sterilization acts primarily by which biochemical process?
- Oxidative cleavage of lipids
- Cross-linking proteins and nucleic acids
- Hydrogen abstraction
- Reducing disulfide bonds
Correct Answer: Cross-linking proteins and nucleic acids
Q9. To reduce flammability during ethylene oxide sterilization, EO is commonly mixed with which diluent gas?
- Oxygen
- Carbon dioxide
- Hydrogen
- Chlorine
Correct Answer: Carbon dioxide
Q10. What does the acronym SAL stand for in sterilization validation?
- Sterility Assurance Level
- Standard Aeration Limit
- Sterilant Application Limit
- Specific Activity Level
Correct Answer: Sterility Assurance Level
Q11. Which parameter is least directly critical for ethylene oxide sterilization efficacy?
- Temperature
- Relative humidity
- Exposure time
- Ambient pH of the sterilizer room
Correct Answer: Ambient pH of the sterilizer room
Q12. Which material class is generally incompatible with vaporized hydrogen peroxide sterilization due to absorption and condensation?
- Metals
- Cellulosic materials (paper, cotton)
- Glass
- Ceramics
Correct Answer: Cellulosic materials (paper, cotton)
Q13. Which gaseous sterilant is classified as a human carcinogen and requires strict controls and aeration?
- Ozone
- Ethylene oxide
- Vaporized hydrogen peroxide
- Carbon dioxide
Correct Answer: Ethylene oxide
Q14. Which biological indicator organism is most commonly used to assess vaporized hydrogen peroxide or plasma sterilization cycles?
- Bacillus anthracis
- Geobacillus stearothermophilus
- Escherichia coli
- Pseudomonas aeruginosa
Correct Answer: Geobacillus stearothermophilus
Q15. What is a principal advantage of gaseous sterilization methods over moist heat (autoclaving)?
- They always require higher temperatures
- They are effective for heat- and moisture-sensitive devices
- They never require monitoring
- They always sterilize liquids effectively
Correct Answer: They are effective for heat- and moisture-sensitive devices
Q16. What is a key disadvantage of ethylene oxide sterilization compared to VHP and plasma?
- Short exposure time
- Formation of toxic residues and long aeration
- Inability to sterilize plastics
- Lack of sporicidal activity
Correct Answer: Formation of toxic residues and long aeration
Q17. Which gaseous sterilant is preferred when minimal chemical residues are required for immediate use of devices?
- Ethylene oxide
- Vaporized hydrogen peroxide
- Formaldehyde
- Chlorine gas
Correct Answer: Vaporized hydrogen peroxide
Q18. Which environmental condition is particularly important to control during ethylene oxide sterilization to ensure microbial inactivation?
- Ultraviolet intensity
- Relative humidity
- Ambient light
- Sound level
Correct Answer: Relative humidity
Q19. What does the D-value represent in sterilization science?
- Decimal point of sterilant concentration
- Time required at a specified condition to reduce the microbial population by one log (90%)
- Distance traveled by sterilant molecules
- Density of the sterilant gas
Correct Answer: Time required at a specified condition to reduce the microbial population by one log (90%)
Q20. What is the Z-value in sterilization terminology?
- Temperature change needed to change the D-value by a factor of ten
- The pH at which sterilization is optimum
- Gas concentration required for sterilization
- Time interval for aeration
Correct Answer: Temperature change needed to change the D-value by a factor of ten
Q21. Historically, which gaseous sterilant was widely used for room and equipment fumigation but is now limited due to toxicity and carcinogenicity?
- Chlorine dioxide
- Formaldehyde
- Nitrogen dioxide
- Carbon dioxide
Correct Answer: Formaldehyde
Q22. Which gaseous sterilant is flammable and explosive when mixed with air, requiring special handling?
- Vaporized hydrogen peroxide
- Ethylene oxide
- Chlorine dioxide
- Ozone
Correct Answer: Ethylene oxide
Q23. Gas plasma sterilization is limited for certain device types because it is less effective in:
- Sterilizing solid flat surfaces
- Penetrating long narrow lumens
- Inactivating vegetative bacteria
- Operating at low temperatures
Correct Answer: Penetrating long narrow lumens
Q24. What does a biological indicator typically contain to assess sterilization performance?
- A chemical dye that changes color
- A measured population of highly resistant spores
- A hygroscopic salt
- An inert plastic strip
Correct Answer: A measured population of highly resistant spores
Q25. Which factor most increases ethylene oxide penetration into porous packaging and packaged loads?
- Decreased gas concentration
- Increased relative humidity
- Lower exposure temperature
- Shorter exposure time
Correct Answer: Increased relative humidity
Q26. Which analytical technique is commonly used to measure residual ethylene oxide on sterilized products?
- Mass spectrometry imaging
- Gas chromatography
- Atomic absorption spectroscopy
- Thin-layer chromatography
Correct Answer: Gas chromatography
Q27. What sterility assurance level (SAL) is commonly targeted for sterile medical devices?
- 10^-3
- 10^-6
- 10^-9
- 10^-1
Correct Answer: 10^-6
Q28. Which gaseous sterilant has been classically used for sterilizing disposable syringes, tubing and heat-sensitive medical devices?
- Chlorine gas
- Ethylene oxide
- Steam
- Dry heat
Correct Answer: Ethylene oxide
Q29. Exposure to which gaseous sterilant can cause polymer aging, loss of plasticizers and changes in elastomer properties?
- Ethylene oxide
- Vaporized hydrogen peroxide
- Nitrogen
- Argon
Correct Answer: Ethylene oxide
Q30. Which sterilization technology uses hydrogen peroxide vapor that is subsequently converted into a low-temperature plasma to achieve sterilization?
- Ethylene oxide chamber sterilization
- Hydrogen peroxide plasma sterilization
- Ozone gaseous sterilization
- Formaldehyde fumigation
Correct Answer: Hydrogen peroxide plasma sterilization
Q31. Which monitoring tool provides immediate visual confirmation of process parameter exposure but not proof of sterility?
- Biological indicator
- Chemical indicator
- Culture-based sterility test
- Endotoxin assay
Correct Answer: Chemical indicator
Q32. Which international standard specifically provides requirements for the development, validation and routine control of ethylene oxide sterilization processes?
- ISO 13485
- ISO 11135
- ISO 9001
- ISO 14971
Correct Answer: ISO 11135
Q33. Which of the following is a process challenge device used in gaseous sterilization validation?
- A chemical compatibility chart
- A simulated load with representative worst-case geometry
- An inert glass coupon
- A paper label
Correct Answer: A simulated load with representative worst-case geometry
Q34. Why is relative humidity often controlled during ethylene oxide and ozone sterilization cycles?
- Humidity dilutes the sterilant
- Moisture facilitates microbial susceptibility and sterilant reactivity
- Humidity cools the sterilizer chamber
- Humidity increases chamber pressure
Correct Answer: Moisture facilitates microbial susceptibility and sterilant reactivity
Q35. What unit is the D-value most commonly expressed in for gaseous sterilization processes?
- Degrees Celsius
- Minutes
- Parts per million (ppm)
- Meters
Correct Answer: Minutes
Q36. Which property of ethylene oxide contributes most to its ability to sterilize wrapped and packaged items?
- High boiling point
- Excellent penetration into porous materials
- Strong UV emission
- Heavy molecular weight preventing diffusion
Correct Answer: Excellent penetration into porous materials
Q37. Which gaseous sterilant is commonly used in controlled room fumigation and surface disinfection and is a strong oxidant that decomposes to oxygen?
- Vaporized hydrogen peroxide
- Ethylene oxide
- Carbon monoxide
- Sulfur dioxide
Correct Answer: Vaporized hydrogen peroxide
Q38. Which sterilization method is most appropriate for electronic medical devices sensitive to heat but requiring low-residue processing?
- Steam autoclave
- Hydrogen peroxide plasma
- Dry heat oven
- Ethylene oxide without aeration
Correct Answer: Hydrogen peroxide plasma
Q39. Which workplace control is essential to protect personnel from exposure to ethylene oxide?
- Personal exposure monitoring and local exhaust ventilation
- Use of open flame to disperse EO
- Increasing room temperature
- Using EO without containment
Correct Answer: Personal exposure monitoring and local exhaust ventilation
Q40. Chlorine dioxide gas is primarily used in sterilization for which application?
- High-temperature steam sterilization
- Environmental and room decontamination, and some equipment sterilization
- Drying pharmaceutical powders
- Increasing shelf-life of plastics
Correct Answer: Environmental and room decontamination, and some equipment sterilization
Q41. Which gaseous sterilization method is generally most compatible with delicate electronic assemblies and optics?
- High-temperature dry heat
- Gas plasma (low-temperature plasma) sterilization
- Ethylene oxide at high humidity
- Ozone at high concentrations
Correct Answer: Gas plasma (low-temperature plasma) sterilization
Q42. Which of the following best describes a chemical indicator used in gaseous sterilization?
- A living microorganism that reports sterility
- A device that changes color when exposed to specific process parameters
- A trap for capturing residual gas
- An electronic logger for temperature only
Correct Answer: A device that changes color when exposed to specific process parameters
Q43. Which documentation concept is essential for gaseous sterilization validation and routine control?
- Random unrecorded cycles
- Defined cycle parameters, BI/Chemical indicator results and traceable records
- No recordkeeping to save costs
- Only verbal approval of cycles
Correct Answer: Defined cycle parameters, BI/Chemical indicator results and traceable records
Q44. Which of these is NOT a recommended practice for loading an ethylene oxide sterilizer?
- Arrange items to allow gas penetration
- Seal porous loads so gas cannot enter
- Avoid overpacking
- Use representative process challenge devices in worst-case positions
Correct Answer: Seal porous loads so gas cannot enter
Q45. Which monitoring parameter must be controlled for ozone sterilization to be effective?
- pH of sterilant
- Relative humidity and ozone concentration
- Magnetic field strength
- Sound frequency
Correct Answer: Relative humidity and ozone concentration
Q46. Which statement about ethylene oxide residue limits and safety is correct?
- No aeration is required after EO treatment
- Residue limits are regulated and aeration is required to reduce toxic residues to acceptable levels
- EO residues are beneficial for packaging shelf-life
- Residue testing is optional and rarely performed
Correct Answer: Residue limits are regulated and aeration is required to reduce toxic residues to acceptable levels
Q47. Which biological indicator result after incubation indicates a failed sterilization cycle?
- No growth after the incubation period
- Visible microbial growth from the BI culture
- Color change in a chemical indicator only
- An empty incubator
Correct Answer: Visible microbial growth from the BI culture
Q48. Which gaseous sterilant is most appropriate for rapid room decontamination of sensitive areas without long-term residues?
- Formaldehyde
- Vaporized hydrogen peroxide
- Ethylene oxide
- Chlorine gas
Correct Answer: Vaporized hydrogen peroxide
Q49. What is the main rationale for performing biological indicator placement at worst-case locations during validation?
- To reduce validation time
- To demonstrate sterilant efficacy under most challenging positions within the load
- To avoid using chemical indicators
- To increase the number of cycles
Correct Answer: To demonstrate sterilant efficacy under most challenging positions within the load
Q50. Which regulatory or quality concept requires that sterilization cycles be routinely monitored and traceable for sterile pharmaceutical devices?
- Good Manufacturing Practice (GMP)
- Random practice testing
- Informal operator checks only
- No monitoring for sterile devices
Correct Answer: Good Manufacturing Practice (GMP)
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