Questions: Sterilization aims to destroy all microorganisms including heat-resistant microbes and their spores. Therefore, what is the range of severe heat employed in sterilization? a) 65-73°C b) 53-62°C c) 89-97°C d) 110-121°C

The answer is the fourth one (or D): $110-121^{\circ} \mathrm{C}$.

Explanation for each option: a) $65-73^{\circ} \mathrm{C}$: This temperature range is typically used for pasteurization, not sterilization. Pasteurization aims to reduce the number of viable pathogens but does not destroy all microorganisms and their spores.

b) $53-62^{\circ} \mathrm{C}$: This temperature range is too low for effective sterilization. It might be used for some forms of pasteurization or other mild heat treatments.

c) $89-97^{\circ} \mathrm{C}$: This range is also insufficient for sterilization. It might be used for high-temperature short-time (HTST) pasteurization but not for complete sterilization.

d) $110-121^{\circ} \mathrm{C}$: This is the correct range for sterilization. Autoclaving, a common sterilization method, typically uses temperatures in this range (specifically around $121^{\circ} \mathrm{C}$) to ensure the destruction of all microorganisms, including heat-resistant spores.

Summary: Sterilization requires severe heat to destroy all microorganisms, including heat-resistant spores. The appropriate temperature range for this process is $110-121^{\circ} \mathrm{C}$, making option D the correct answer.