Final answer:
The statement regarding effusive material forming lava tubes with a smooth and ropy look being true is accurate. This is characteristic of basaltic pahoehoe lava flows, leading to the formation of extrusive igneous rocks, such as basalt, which are fine-grained due to rapid cooling.
Step-by-step explanation:
The effusive material that forms lava tubes where fluid lava flows through the outer cooled rock crust and has a smooth and ropy look is true. This is typical of pahoehoe lava flows, a form of basaltic lava that moves quickly and can easily flow over long distances. The rapid movement and cooling of the lava often result in the creation of tubes as the surface cools and hardens while the molten lava continues to flow beneath it.
When this type of lava extrudes onto the Earth's surface, it cools rapidly, forming extrusive igneous rocks, which are usually very fine-grained due to the short period available for crystal formation. Some examples of extrusive igneous rocks include rhyolite, basalt, and volcanic glass like obsidian.