Final answer:
The correct answer to the question is option C) Nation state, which refers to a political unit where the population shares a common cultural identity, including language and culture.
Step-by-step explanation:
States whose populations share a sense of cultural identity, which usually includes a language and a culture, are best described as nation-states. This concept denotes a political unit that not only exercises control over a defined territory but also embodies a population connected by common cultural elements such as ethnicity, language, or religion. These nation-states became especially significant in the nineteenth century when nationalist movements sought to align territorial states with ethnolinguistic and cultural nations, creating a congruence between the nation (people with a shared identity) and the state (political and administrative institution).
In the context of a nation-state, a shared identity based on common history, religion, or ethnic background is fundamental to the cohesion and legitimacy of the state itself. Therefore, option C) Nation state is the correct answer to define states whose populations share a sense of cultural identity, usually including a language and culture.