Which igneous rock is cooled the slowest Gabro or Granite?

Answer 1

The type of igneous rock formed depends more on the composition of the magma or lava that formed it than it does on the speed at which it cooled (notable exceptions include obsidian, which is flash cooled). To determine which cooled faster look at the coarseness of the rock. Large crystalline particles are formed by slower cooling liquid since the molecules had more time to arrange into crystals.

That being said, Granite is more likely than Gabbro to have cooled away from water and therefore slower.