Volcanic eruptions do not occur in the

Volcanic eruptions are concentrated along tectonic plate boundaries and oceanic spreading ridges rather than in stable intraplate seas [2]. The Baltic Sea lies well within the Eurasian plate and lacks local volcanic centers; tephra (volcanic ash) found in Baltic sediments is airborne fallout transported from distant eruptions (not evidence of local eruptions). By contrast, the Caribbean Sea overlies the active Lesser Antilles volcanic arc (subduction-related volcanism), and the Caspian region hosts numerous mud- and hydrocarbon-related volcanoes onshore and offshore; both experience volcanic or volcanogenic activity. Hence, among the options given, the Baltic Sea is the basin where volcanic eruptions do not occur.

Sources

1. [1] https://oceanservice.noaa.gov/facts/volcanoes.html
2. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Distribution of Volcanoes in the World > p. 12