Antimicrobials: Hydrogen peroxide* MCQs With Answer

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Antimicrobials: Hydrogen peroxide* MCQs With Answer

Hydrogen peroxide is a versatile antimicrobial and oxidizing agent widely covered in B.Pharm curricula. This introduction explains key concepts including mechanism of action (generation of reactive oxygen species), spectrum of activity (bactericidal, fungicidal, virucidal; limited sporicidal effect), concentration-dependent uses (3% antiseptic, 30% industrial, vaporized H2O2 for sterilization), stabilization and incompatibilities, assay methods, and safety handling. Understanding catalase/peroxidase interactions, formulation stabilizers, decomposition kinetics, and clinical versus industrial applications is essential for pharmacists in practice and research. These MCQs will help reinforce mechanistic and practical knowledge for exam preparation and professional competence. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is the primary mechanism by which hydrogen peroxide exerts its antimicrobial effect?

  • Chelation of essential metal ions in microbes
  • Generation of reactive oxygen species causing oxidative damage
  • Disruption of membrane lipopolysaccharides through surfactant action
  • Interference with peptidoglycan cross-linking

Correct Answer: Generation of reactive oxygen species causing oxidative damage

Q2. Which microbial enzyme most directly reduces the efficacy of hydrogen peroxide?

  • Beta-lactamase
  • Catalase
  • DNA gyrase
  • Transpeptidase

Correct Answer: Catalase

Q3. Which concentration of hydrogen peroxide is commonly used as a topical antiseptic?

  • 0.3% w/v
  • 3% w/v
  • 30% w/v
  • 50% w/v

Correct Answer: 3% w/v

Q4. Vaporized hydrogen peroxide (VHP) is mainly used for which application in healthcare facilities?

  • Hand antisepsis
  • Surface sterilization of rooms and equipment
  • Wound irrigation
  • Oral antiseptic mouthwash

Correct Answer: Surface sterilization of rooms and equipment

Q5. Which reactive species is primarily formed from hydrogen peroxide decomposition that damages cellular components?

  • Superoxide anion (O2•–)
  • Hydroxyl radical (•OH)
  • Nitric oxide (NO•)
  • Singlet oxygen (1O2)

Correct Answer: Hydroxyl radical (•OH)

Q6. Which of the following statements about hydrogen peroxide and spores is correct?

  • Hydrogen peroxide at 3% is rapidly sporicidal
  • Spores are easily inactivated by short exposures to H2O2
  • High concentration or vaporized H2O2 with prolonged contact is needed for sporicidal activity
  • Hydrogen peroxide cannot affect spores under any condition

Correct Answer: High concentration or vaporized H2O2 with prolonged contact is needed for sporicidal activity

Q7. Which metal ion commonly catalyzes the decomposition of hydrogen peroxide?

  • Calcium (Ca2+)
  • Potassium (K+)
  • Iron (Fe2+/Fe3+)
  • Sodium (Na+)

Correct Answer: Iron (Fe2+/Fe3+)

Q8. Which stabilizer is often added to commercial hydrogen peroxide solutions to reduce decomposition?

  • Sodium chloride
  • EDTA (ethylenediaminetetraacetic acid)
  • Calcium carbonate
  • Sucrose

Correct Answer: EDTA (ethylenediaminetetraacetic acid)

Q9. Which assay method is commonly used to determine hydrogen peroxide concentration in pharmaceutical preparations?

  • Potentiometric titration with NaOH
  • Permanganate titration in acidic medium
  • Gravimetric analysis after precipitation
  • UV-visible spectrophotometry at 280 nm without reagents

Correct Answer: Permanganate titration in acidic medium

Q10. In iodometric determination of hydrogen peroxide, which reagent is first oxidized by H2O2 to liberate iodine?

  • Sodium thiosulfate
  • Potassium iodide
  • Ammonium molybdate
  • Phenolphthalein

Correct Answer: Potassium iodide

Q11. Which property makes hydrogen peroxide a safer option than some halogen disinfectants for residue concerns?

  • It forms stable long-lived toxic byproducts
  • It decomposes to water and oxygen without halogen residues
  • It leaves chlorinated organic residues
  • It produces heavy metal contamination

Correct Answer: It decomposes to water and oxygen without halogen residues

Q12. Which pH range favors stability of hydrogen peroxide solutions?

  • Strongly acidic (pH 1–2)
  • Neutral to slightly acidic (pH 4–7)
  • Strongly alkaline (pH 11–13)
  • Extremely alkaline (pH >13)

Correct Answer: Neutral to slightly acidic (pH 4–7)

Q13. Which packaging material is generally preferred for storing aqueous hydrogen peroxide to minimize decomposition?

  • Copper containers
  • Clear glass bottles exposed to light
  • Opaque high-density polyethylene (HDPE) containers with UV protection
  • Aluminum cans with metal lids

Correct Answer: Opaque high-density polyethylene (HDPE) containers with UV protection

Q14. Which of the following is a major limitation of hydrogen peroxide as an antiseptic for deep wound cleaning?

  • It is highly selective for anaerobes only
  • It is neutralized quickly by catalase in tissues and fluids
  • It forms a persistent film that delays healing
  • It causes permanent tissue staining

Correct Answer: It is neutralized quickly by catalase in tissues and fluids

Q15. Combining hydrogen peroxide with acetic acid can lead to formation of which potent disinfectant?

  • Peracetic acid (peroxyacetic acid)
  • Sodium hypochlorite
  • Chloramine-T
  • Glutaraldehyde

Correct Answer: Peracetic acid (peroxyacetic acid)

Q16. Which statement best describes hydrogen peroxide’s activity against viruses?

  • Ineffective against enveloped viruses
  • Generally effective against both enveloped and non-enveloped viruses depending on concentration and contact time
  • Only effective when combined with alcohol
  • Effective only at pH >10

Correct Answer: Generally effective against both enveloped and non-enveloped viruses depending on concentration and contact time

Q17. Which is a common indicator of hydrogen peroxide decomposition in storage?

  • Increase in viscosity
  • Decrease in solution temperature
  • Evolution of oxygen gas and bubbling in closed containers
  • Development of red color

Correct Answer: Evolution of oxygen gas and bubbling in closed containers

Q18. What is the primary reason metal catalysts accelerate hydrogen peroxide decomposition?

  • They increase the solution pH
  • They provide electron transfer sites facilitating breakdown into radicals and O2
  • They bind to water molecules making H2O2 unstable
  • They complex with organic stabilizers

Correct Answer: They provide electron transfer sites facilitating breakdown into radicals and O2

Q19. Which safety hazard is most relevant when handling concentrated hydrogen peroxide (>30%)?

  • It is highly flammable like gasoline
  • It is a strong oxidizer that can cause severe burns and accelerate combustion
  • It is an inert gas at room temperature
  • It is a potent narcotic

Correct Answer: It is a strong oxidizer that can cause severe burns and accelerate combustion

Q20. In a formulation containing metal traces, which additive would you include to chelate metal ions and stabilize hydrogen peroxide?

  • Ethanol
  • EDTA or its salts
  • Calcium chloride
  • Magnesium sulfate

Correct Answer: EDTA or its salts

Q21. Which analytical technique can selectively quantify hydrogen peroxide at low concentrations using a colorimetric reaction?

  • FTIR spectroscopy without reagents
  • Peroxidase-mediated colorimetric assay (e.g., HRP/ABTS)
  • Direct refractometry
  • X-ray diffraction

Correct Answer: Peroxidase-mediated colorimetric assay (e.g., HRP/ABTS)

Q22. Which material is most likely to be corroded by hydrogen peroxide solutions over time?

  • Stainless steel if contaminated with transition metals
  • Pure gold
  • PTFE (Teflon)
  • Glass with neutral pH

Correct Answer: Stainless steel if contaminated with transition metals

Q23. Which factor does NOT significantly affect the antimicrobial efficacy of hydrogen peroxide?

  • Organic load or presence of blood
  • Contact time
  • Ambient light intensity at very low concentrations
  • Presence of catalase-positive organisms

Correct Answer: Ambient light intensity at very low concentrations

Q24. For disinfection of endoscopes, which form of H2O2-based sterilant is commonly used?

  • Undiluted 3% topical solution
  • Hydrogen peroxide combined with peracetic acid (accelerated hydrogen peroxide) or VHP systems
  • Pure dry H2O2 crystals
  • H2O2 mixed with isopropyl alcohol only

Correct Answer: Hydrogen peroxide combined with peracetic acid (accelerated hydrogen peroxide) or VHP systems

Q25. Which microbial component is particularly susceptible to oxidative damage by hydrogen peroxide?

  • Ribosomal RNA only
  • Cellular lipids, proteins and DNA
  • Only the peptidoglycan layer
  • Only the capsule polysaccharide

Correct Answer: Cellular lipids, proteins and DNA

Q26. When formulating hydrogen peroxide in a pharmaceutical product, why is light exclusion important?

  • Light increases product viscosity
  • Light can accelerate photodecomposition of H2O2
  • Light causes immediate freezing of solution
  • Light makes the solution alkaline

Correct Answer: Light can accelerate photodecomposition of H2O2

Q27. Which standard laboratory control would indicate interference by catalase in an efficacy test of hydrogen peroxide?

  • Using catalase-treated bacterial suspension as a test sample
  • Testing at pH 9 only
  • Measuring color change with phenolphthalein
  • Incubating samples on ice

Correct Answer: Using catalase-treated bacterial suspension as a test sample

Q28. Accelerated hydrogen peroxide (AHP) typically contains which additional component to broaden efficacy?

  • Chlorine bleach
  • Surfactants and organic acids to enhance activity
  • High concentrations of sodium hydroxide
  • Inert oils to reduce evaporation

Correct Answer: Surfactants and organic acids to enhance activity

Q29. Which of the following is a regulatory consideration when using hydrogen peroxide sterilization for medical devices?

  • Compatibility of device materials with H2O2 and verification of residue removal
  • Requirement to sterilize using only heat methods
  • Universal prohibition of H2O2 in all regulated devices
  • No need for validation or biological indicators

Correct Answer: Compatibility of device materials with H2O2 and verification of residue removal

Q30. What is the role of peroxidase enzymes in biological systems relative to hydrogen peroxide?

  • They synthesize hydrogen peroxide from amino acids
  • They catalyze the reduction of H2O2, limiting oxidative damage
  • They convert H2O2 into stronger oxidants only
  • They store H2O2 as an energy reserve

Correct Answer: They catalyze the reduction of H2O2, limiting oxidative damage

Q31. Which test organism is commonly used to evaluate sporicidal activity of hydrogen peroxide sterilization systems?

  • Escherichia coli
  • Bacillus subtilis spores or Geobacillus stearothermophilus spores
  • Saccharomyces cerevisiae yeast cells
  • Staphylococcus epidermidis

Correct Answer: Bacillus subtilis spores or Geobacillus stearothermophilus spores

Q32. How does organic matter affect hydrogen peroxide disinfection?

  • Organic matter universally enhances H2O2 activity
  • Organic matter can consume oxidant and reduce antimicrobial efficacy
  • Organic matter converts H2O2 into hypochlorous acid
  • Organic matter has no effect on oxidizing agents

Correct Answer: Organic matter can consume oxidant and reduce antimicrobial efficacy

Q33. What is a common indicator used to verify exposure during vaporized hydrogen peroxide sterilization cycles?

  • Thermocouple readings only
  • Biological indicators containing resistant spores
  • pH strips
  • Viscosity changes of a test fluid

Correct Answer: Biological indicators containing resistant spores

Q34. Which of the following best describes the environmental breakdown products of hydrogen peroxide?

  • Persistent chlorinated organics
  • Benign water and oxygen
  • Toxic heavy metals
  • Long-lived peroxides in soil

Correct Answer: Benign water and oxygen

Q35. In pharmaceutical compounding, why must metal utensils be avoided with hydrogen peroxide?

  • Metal utensils will form insoluble complexes that preserve H2O2
  • Metal contact can catalyze rapid decomposition of hydrogen peroxide
  • Metals increase the viscosity of H2O2 solutions
  • Metals convert H2O2 into ethanol

Correct Answer: Metal contact can catalyze rapid decomposition of hydrogen peroxide

Q36. Which of the following organisms is most likely to survive short exposure to 3% hydrogen peroxide due to catalase activity?

  • Streptococcus pyogenes (catalase-negative)
  • Staphylococcus aureus (catalase-positive)
  • Clostridium tetani spores
  • Mycoplasma species

Correct Answer: Staphylococcus aureus (catalase-positive)

Q37. What is a principal benefit of hydrogen peroxide-based disinfectants labeled as “no-rinse” for food contact surfaces?

  • They leave persistent toxic residues
  • They break down into non-toxic products so rinsing may be unnecessary
  • They generate chlorine gas that sanitizes further
  • They create a protective polymer film

Correct Answer: They break down into non-toxic products so rinsing may be unnecessary

Q38. Which kinetic order commonly describes the decomposition of hydrogen peroxide in presence of catalytic surfaces at constant conditions?

  • Zero-order kinetics independent of H2O2 concentration
  • First-order kinetics with respect to H2O2 concentration
  • Second-order kinetics with respect to water only
  • Fractional-order kinetics unrelated to catalyst

Correct Answer: First-order kinetics with respect to H2O2 concentration

Q39. Which monitoring parameter is important during VHP sterilization to ensure adequate microbicidal activity?

  • Relative humidity only
  • H2O2 vapor concentration and exposure time
  • Color change of metal surfaces
  • Atmospheric CO2 concentration

Correct Answer: H2O2 vapor concentration and exposure time

Q40. In wound care, what is a documented adverse effect of frequent hydrogen peroxide application?

  • Enhanced fibroblast proliferation and faster healing
  • Delayed wound healing due to cytotoxicity to host cells
  • Permanent antimicrobial immunity
  • Conversion of wound to anaerobic environment

Correct Answer: Delayed wound healing due to cytotoxicity to host cells

Q41. Which chemical test would be interfered by residual detergent when assaying hydrogen peroxide in cleaning solutions?

  • Permanganate titration due to organic reducing agents consuming oxidant
  • Gravimetric precipitation unaffected
  • Direct pH measurement only
  • Thermogravimetric analysis is unaffected

Correct Answer: Permanganate titration due to organic reducing agents consuming oxidant

Q42. Which storage condition will most rapidly accelerate H2O2 degradation?

  • Cool, dark storage in stabilized containers
  • Warm temperatures with sunlight exposure and metal contamination
  • Refrigeration at 4°C, protected from light
  • Storage under nitrogen in amber bottles

Correct Answer: Warm temperatures with sunlight exposure and metal contamination

Q43. Which combination is often used to increase disinfectant potency while maintaining lower H2O2 concentrations?

  • H2O2 with surfactants and organic acids (accelerated H2O2)
  • H2O2 with heavy metals
  • H2O2 mixed with concentrated bleach
  • H2O2 and sugar syrups

Correct Answer: H2O2 with surfactants and organic acids (accelerated H2O2)

Q44. What is the recommended immediate action if concentrated hydrogen peroxide spills on skin?

  • Rub vigorously with alcohol
  • Rinse immediately with copious water and remove contaminated clothing
  • Neutralize with sodium hydroxide on skin
  • Cover with oil and seek no further aid

Correct Answer: Rinse immediately with copious water and remove contaminated clothing

Q45. Which of the following is a valid reason for preferring vaporized hydrogen peroxide over ethylene oxide for some sterilization tasks?

  • VHP is highly flammable and therefore preferred
  • VHP leaves no toxic residues and has shorter cycle times for many items
  • Ethylene oxide is always faster and safer
  • VHP is ineffective against all spores compared to EtO

Correct Answer: VHP leaves no toxic residues and has shorter cycle times for many items

Q46. Which of these tests helps assess whether hydrogen peroxide has penetrated a porous load during sterilization?

  • Visual inspection only
  • Use of chemical indicators and biological indicators placed within the porous load
  • Measuring ambient temperature outside the chamber
  • Monitoring pH of the chamber air

Correct Answer: Use of chemical indicators and biological indicators placed within the porous load

Q47. Which statement is true regarding hydrogen peroxide’s role as a preservative in pharmaceutical formulations?

  • H2O2 is commonly used as a long-term preservative in aqueous formulations
  • H2O2 is generally unsuitable as a preservative due to instability and reactivity with formulation components
  • H2O2 is inert and does not react with excipients
  • H2O2 functions as an anti-foaming agent rather than preservative

Correct Answer: H2O2 is generally unsuitable as a preservative due to instability and reactivity with formulation components

Q48. Which property of hydrogen peroxide contributes to its role in bleaching pharmaceutical excipients or APIs?

  • Its basic pH only
  • Its oxidative capacity to break chromophores in organic molecules
  • Its ability to form complexes with proteins that color them
  • Its reducing properties

Correct Answer: Its oxidative capacity to break chromophores in organic molecules

Q49. Which of the following organisms is used as a biological indicator for vaporized hydrogen peroxide sterilization validation?

  • Escherichia coli vegetative cells
  • Geobacillus stearothermophilus spores
  • Candida albicans yeast
  • Human skin flora

Correct Answer: Geobacillus stearothermophilus spores

Q50. Which precaution is important when disposing of concentrated hydrogen peroxide waste from a compounding facility?

  • Neutralize with organic solvents before release
  • Dilute and neutralize appropriately, avoid mixing with incompatible reducing agents or combustibles, and follow local regulations
  • Pour directly into general sewage without treatment
  • Store indefinitely in open containers

Correct Answer: Dilute and neutralize appropriately, avoid mixing with incompatible reducing agents or combustibles, and follow local regulations

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