The igneous rock you are describing, which floats due to trapped air bubbles, is likely to be classified as extrusive. This is because extrusive igneous rocks form from lava that cools and solidifies quickly on the Earth's surface, often resulting in a texture that may include trapped gas bubbles.
In contrast, intrusive igneous rocks form deeper underground where the cooling process is slower, allowing larger crystals to develop, leading to a coarse texture.
So, to accurately classify the rock you mentioned, "extrusive" would be the correct term.