The concept of political sovereignty refers to the supreme authority or power to govern a territory or state. It is the idea that the ultimate decision-making authority rests with a single entity or government. In the given question, the correct answer is option 3, Rousseau. Jean-Jacques Rousseau, a philosopher of the Enlightenment period, advocated for the concept of political sovereignty in his book "The Social Contract." He argued for the idea that political authority comes from the consent of the governed, and that the people are the ultimate source of sovereignty. Rousseau`s ideas have had a significant influence on democratic theories and the development of modern nation-states. It is important to note that while other philosophers, like Plato, John Locke, and Austin, have also contributed to political theory, they may have advocated for different concepts or theories of sovereignty.