Final answer:
Based on the eruption of Mt. Vesuvius in 79 C.E. and Pompeii being buried in ash, basaltic (mafic) lava would be the least expected material to find because Vesuvius's eruptions produce more viscous magmas that are felsic in composition.
Step-by-step explanation:
On the basis of the violent explosion of Mt. Vesuvius in 79 C.E. and the subsequent burial of Pompeii under ash, one would LEAST expect to find basaltic (mafic) lava at Vesuvius. Mt. Vesuvius is known for its highly explosive eruptions producing more viscous magmas like rhyolite, thus basaltic lava, which is typically associated with less explosive, effusive eruptions, would not be anticipated. The eruption produced material such as ignimbrite, a highly indurated, welded tuff associated with pyroclastic flows; lapilli or volcanic ash, and rhyolite lava which is felsic in composition and associated with explosive volcanic activity.