Explanation:

- Mortality refers to the state of being subject to death or the incidence of death within a population.

- Option 1: Fatality is synonymous with death, highlighting the result of a deadly event, and aligns with the concept of mortality.

- Option 2: Lethality refers to the ability or capacity to cause death. It is closely associated with how deadly something is, again aligning with mortality.

- Option 3: Death is the cessation of life, directly fitting under the umbrella of mortality.

- Option 4: Birth signifies the opposite of death: the beginning of life, and therefore the antonym of mortality.

? Option 4: Birth is indeed the correct antonym.