MCQs (Questions and Answers) on Sterilization & Disinfection Methods

1. Temperature and duration in Flash method of Pasteurization is
A) 62.9°C, 30 min
B) 71.6°C, 30 min
C) 71.6°C, 15 seconds
D) 62.9°C, 15 seconds
✅ Correct answer is C. 71.6°C for 15 seconds (HTST pasteurization).
2. Concentration range for ethylene oxide sterilization is
A) 15–100 mg/L
B) 800–1200 mg/L
C) 120–180 mg/L
D) 1000–1200 mg/L
✅ Correct answer is B. 800–1200 mg/L.
3. Browne’s tubes are indicators for
A) Heat sterilization
B) Radiation sterilization
C) Gaseous sterilization
D) Filtration sterilization
✅ Correct answer is A. Heat sterilization.
4. Royce sachet is indicator for
A) Formaldehyde
B) β-propiolactone
C) Isopropyl alcohol
D) Ethylene oxide
✅ Correct answer is D. Ethylene oxide.
5. Recommended time and pressure for autoclave sterilization of media
A) 15 min, 10 lbs
B) 60 min, 5 lbs
C) 15 min, 15 lbs
D) 15 min, 20 lbs
✅ Correct answer is C. 15 minutes at 15 lbs pressure (121°C).
6. Sterilization potency is highest in
A) Filtration
B) Hot air oven
C) Ultrasound waves
D) Autoclaving
✅ Correct answer is D. Autoclaving.
7. Formalin and KMnO₄ required for 1000 cu ft area
A) 280 ml formalin + 150 g KMnO₄
B) 300 ml formalin + 150 g KMnO₄
C) 180 ml formalin + 100 g KMnO₄
D) 80 ml formalin + 150 g KMnO₄
✅ Correct answer is A. 280 ml formalin + 150 g KMnO₄.
8. Suitable pore size for bacterial filtration
A) 0.22 mm
B) 0.45 nm
C) 0.22 μm
D) 30 μm
✅ Correct answer is C. 0.22 μm.
9. Time required to destroy 90% organisms is called
A) D value
B) Z value
C) F value
D) Q10 value
✅ Correct answer is A. D value.
10. Biological indicator for ionizing radiation
A) Bacillus subtilis
B) Bacillus pumilus
C) Salmonella typhi
D) Serratia marcescens
✅ Correct answer is B. Bacillus pumilus.
11. Suitable method of sterilization of powders
A) Autoclaving
B) Hot air oven
C) UV radiation
D) Gaseous
✅ Correct answer is B. Hot air oven.
12. Temperature change to produce 10-fold change in D value
A) D value
B) Z value
C) F value
D) Q10 value
✅ Correct answer is B. Z value.
13. Mechanism of action of ethylene oxide
A) Alkylation of molecules
B) Oxidation
C) Denaturing of proteins
D) Membrane disruption
✅ Correct answer is C. Denaturing of proteins.
14. Best method of sterilizing disposable syringes
A) Autoclave
B) Boiling
C) Hot air oven
D) Gamma radiation
✅ Correct answer is D. Gamma radiation.
15. Temperature and duration in Holder’s method of pasteurization
A) 62.9°C, 30 min
B) 63°C, 90 min
C) 71.6°C, 15 min
D) 62.9°C, 15 sec
✅ Correct answer is A. 62.9°C for 30 minutes.
16. Pressure of 15 psi in autoclave equals
A) 123°C
B) 72°C
C) 121°C
D) 160°C
✅ Correct answer is C. 121°C.
17. Bubble point pressure test validates
A) Autoclave
B) Hot air oven
C) Radiation
D) Filtration
✅ Correct answer is D. Filtration.
18. Suitable method for sterilization of syringes
A) Hot air oven
B) Autoclave
C) Filtration
D) Radiation
✅ Correct answer is D. Radiation.
19. Sterilization of catgut and gloves is done by
A) X-rays
B) Gamma radiation
C) IR waves
D) Microwaves
✅ Correct answer is B. Gamma radiation.
20. Recommended time and temperature for hot air oven sterilization
A) 160°C, 120 min
B) 180°C, 120 min
C) 160°C, 60 min
D) 160°C, 180 min
✅ Correct answer is A. 160°C for 120 minutes.

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