Mariupol is a city located in eastern Ukraine, and it is often mentioned in the news due to its role in the ongoing conflict between Russia and Ukraine. The options in this question refer to the geographical location of Mariupol, particularly in terms of which Sea it`s situated on the coast of.

Option 1 (Aral Sea) is incorrect, as the Aral Sea is situated between Kazakhstan and Uzbekistan, in Central Asia, far removed from this area.

Option 2 (Baltic Sea) is incorrect as well, as the Baltic Sea is located in Northern Europe, and Ukraine doesn`t have a coastline on this Sea.

Option 3 (Caspian Sea) is also incorrect, this Sea is the world`s largest inland body of water, located between Europe and Asia, its coastlines are shared by five countries, none of which is Ukraine.

Option 4 (Sea of Azov) is indeed the correct answer, as Mariupol is situated on the north coast of the Sea of Azov, an arm of the Black Sea, this sea is bounded to the east by Russia and to the west by Ukraine, precisely where Mariupol lies.