The southern part of Eastern Europe, or Southeastern Europe, is the most mountainous part of Eastern Europe.
No. It is just a term for countries that are in the eastern part of Europe. Europe is one continent.
eastern europe - apex
Iran is in Asia (Middle East), not Eastern Europe.
Eastern Europe.
No. Most of Russia is in Asia. The part that is in Europe is in eastern Europe.
The Black Sea is most associated with Eastern Europe.
It is sort of central-Eastern Europe.
Bulgaria is a part of Eastern Europe. However, if Europe was split into its 5 regions, then Bulgaria is a part of Southern Europe (you could go even further from there and say Southeastern Europe).
which parts of eastern europe are sparsely or less populated
It is in the southeast of Europe. See the map at the related link below.
Europe, Germany is concidered part of Eastern Europe