To answer this question we need to analyze each statement.
The members are geographically isolated from each other. This is not correct, because if each member is isolated there would be no reproduction and the population would be extinct in a generation period.
The members are reproductively isolated from each other. This is not correct as it would happen a very similar scenario depicted in the previous statement.
The members are genetically identical to each other. This is not correct as the majority of populations seek out outcrossing, this scenario occurs very rarely in some plants that self-pollinate however is not common.
The members are all of the same species. This statement is correct as populations are composed of organisms belonging to the same species, when we have several species or populations we are talking of communities.