The correct answer is Finland.
About 5,5 million of people live in Finland and the average population density is 17 inhabitants pro square kilometer. Finland is the third most sparsely populated country in Europe after Iceland and Norway. About 85% of Finland's population lives in towns and there are vast areas with no inhabitants at all.
Finland's scarce population is the result of very limited immigrants influx, low birth rates and somehow difficult living conditions in some remote areas. On the other hand, Finland is one of the most prosperous countries in the world, with an excellent education system.