The correct answer is option 2, Hungary.

A landlocked country is a country that does not have direct access to the sea or any ocean. In this question, we are asked to determine which one of the given countries is landlocked.

Option 1, Bulgaria, is not landlocked. It is located in Southeastern Europe and has a coastline on the Black Sea, so it has access to the sea.

Option 2, Hungary, is the correct answer because it is a landlocked country. Hungary is located in Central Europe and does not have any coastlines or access to any sea or ocean.

Option 3, Romania, is not landlocked. It is located in Southeastern Europe and has a coastline on the Black Sea, so it has access to the sea.

Option 4, Ukraine, is also not landlocked. It is located in Eastern Europe and has coastlines on both the Black Sea and the Sea of Azov, so it has access to the sea.

In summary, the only country among the given options that is landlocked is Hungary.