Final answer:
The Iskar River, which originates in the Balkan Mountains and flows through Sofia, is located in Bulgaria, where it eventually empties into the Danube River.
Step-by-step explanation:
The country that has the Iskar River, which rises in the Balkan Mountains, passes through Sofia, and empties into the Danube River is Bulgaria. The Iskar River is the longest river that runs entirely within the borders of Bulgaria. Rising in the Balkans, specifically in the Rila Mountains, it flows through the Bulgarian capital of Sofia and then meanders northward until it joins the Danube, which is one of Europe's major waterways.
The Danube River itself serves as a significant geographical feature, marking the border between Bulgaria and its northern neighbor, Romania.
Moreover, the river is pivotal for commerce, agriculture, and ecosystems across the region. Bulgaria's diverse landscapes, which include not just river valleys but also plains and mountains, contribute to the country's rich agricultural productivity and natural resource wealth.