The maximum number of individuals of a population that can be sustained in a given habitat represents its _____________.

The correct option is C carrying capacity
For any population in natural habitat, the resources for growth are finite and become limiting sooner or later. The maximum number of individuals of a population that can be sustained in a given habitat is known as its carrying capacity (K).

Population density is the number of individuals of a species per unit area.

Intrinsic rate of natural increase or ‘r’ is the difference between number of births and the number of deaths per year. It can be expressed as
r = (b - d)
where b is birth rate
d is death rate

Darwinian fitness or reproductive fitness is the ability of an organism to survive and reproduce in a certain environment, compared to other individuals. Each population evolves to maximize their reproductive fitness in a specific habitat.