Time (in min) required to kill a known population of microorganism under certain conditions at given lethal time is:

Correct option is D

The  F value represents the time required to kill a known population of microorganisms at a specific temperature. It is used in food processing and microbiology to measure the effectiveness of a sterilization process.
Examine each option:
(a) C value: Incorrect; refers to the concentration of the microbial load, not the time for microbial death.
(b) D value: Incorrect; represents the time required to reduce the microbial population by 90% (or one log reduction).
(c) Z value: Incorrect; indicates the temperature change needed to change the D value by a factor of 10.
(d) F value: Correct; measures the time required to achieve a specified level of microbial death under given conditions.
(e) A value: Incorrect; not commonly used in this context.