**Core Concept**
Autoclaving is a method of sterilization that uses high-pressure steam to kill microorganisms. The effectiveness of autoclaving depends on the temperature and time of exposure.

**Why the Correct Answer is Right**
The correct answer is B. 121°C temperature for 15 min because this combination of temperature and time is sufficient to achieve sterilization. Autoclaving involves the use of saturated steam at 121°C, which is the temperature at which the steam is in equilibrium with water. The 15-minute exposure time is necessary to ensure that all microorganisms are killed, including bacterial spores, which are the most resistant forms of life. The temperature and time of autoclaving can be modified, but 121°C for 15 min is the standard condition required for effective sterilization.

**Why Each Wrong Option is Incorrect**
**Option A:** 121°C temperature for 20 min is not the standard condition for autoclaving, and a longer exposure time may not be necessary for effective sterilization.
**Option C:** 100°C temperature for 60 min is below the standard temperature for autoclaving, and a longer exposure time may not be sufficient to achieve sterilization.
**Option D:** 100°C temperature for 90 min is also below the standard temperature for autoclaving, and a longer exposure time may not be sufficient to achieve sterilization.

**Clinical Pearl / High-Yield Fact**
It is essential to note that autoclaving is not effective for all types of materials, such as certain plastics, glassware, and biological samples. These materials may require alternative methods of sterilization, such as dry heat or chemical disinfection.

**✓ Correct Answer: B. 121°C temperature for 15 min**