The northern European plain goes through Sweden, Finland, Norway, Germany, Denmark, and a few more I can't remember on the top of my head.
Yes they are. They are the part of the Alps that run through Switzerland. The Alps as a whole run through a number of European countries.
You need to specify what you are referring to if you want to make it possible to answer your question.
Belarus, Poland, and Russia
The Balkans run through countries such as Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Kosovo, Albania, North Macedonia, Greece, Bulgaria, and Romania.
Through Germany, Austria, Slovakia, Hungary Serbia., Bulgaria. Moldova, Ukraine and Romania
"90 degrees north" is the definition of the north pole. It's a single point which stays right there and does not run, and is not associated with any one specific continent.
Only Costa Rica.
The Ural Mountains run through the countries of Russia and Kazakhstan.
There are no countries on Antarctica.
The Alps run through eight countries in south-central Europe. They start at Mediterranean sea and run north following the border between France and Italy. They then run east through Switzerland, Liechtenstein, Austria, Germany, Monaco, and Slovenia.
The E.U. is run through seven institutions. These are the Council of the European Union, Court of Justice of the European Union, European Central Bank, European Commission, European Council, European Court of Auditors, and European Parliament.