Which of these seas does not border the Balkan Peninsula?

Tyrrhenian Sea does not border the Balkan Peninsula. The Tyrrhenian Sea is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenian people identified with the Etruscans of Italy.

The Balkans, also known as the Balkan Peninsula, is a geographic area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the whole of Bulgaria. The Balkan Peninsula is bordered by the Adriatic Sea in the northwest, the Ionian Sea in the southwest, the Aegean Sea in the south, the Turkish Straits in the east, and the Black Sea in the northeast. The northern border of the peninsula is variously defined. The highest point of the Balkans is Mount Musala, 2,925 metres (9,596 ft), in the Rila mountain range, Bulgaria.