Final answer:
Effusive eruptions occur with magma that has a low silica composition due to its lower viscosity, allowing for a gentle flow.
Step-by-step explanation:
An effusive eruption is most likely to result from magma with a low silica composition. High viscosity and high silica content, characteristics of rhyolitic magma, lead to more explosive eruptions, as the magma is thicker and has a harder time flowing. In contrast, magma with low silica content, such as basalt, has lower viscosity, allowing it to flow more easily and result in an effusive eruption.