Answer:
B. The average number in a certain area
Step-by-step explanation:
Population density is calculated by taking the total area of a region in question and dividing it by the total number of people that live in that area. The result will give the average number of inhabitants per square kilometre, mile, acre, meter, etc. While the population density of an entire country is not a very accurate means of knowing the population density of that countries capital city, it does given an idea of how much land is available in the country per inhabitant.