A nation-state is defined by population, territory, government, and sovereignty. Option A is correct.
A nation state is understood as a state in which the vast majority shares the same culture and is conscious of it. It refers to an ideal in which cultural boundaries match up with political ones.
A population is the number of people living in a particular territory or place.
A territory is the place or the land which is run by a particular ruler.
A sovereignty refers to the supreme power or the authority of common people.