Which of these is defined by population, territory, government, and sovereignt?

a nation-state

b civilization

c parliament

d district

e federation

A nation-state is defined by population, territory, government, and sovereignty. A nation state is a geographical area that can be identified as deriving its political legitimacy from serving as a sovereign nation.

The correct answer is a nation-state

A parliament is a representative body that governs a territory while a district is a part of a state. Federations are organizations of multiple states such as the United States of America, while a civilization revolves around population, not over governments or territories. Nation-states are what you described in your question.