Why is helium used in diving apparatus?

Explanation

Helium is less soluble in blood than nitrogen. So a mixture `O_2`and He is used in diving apparatus. If air is used nitrogen dissolves in blood under the high pressure present in the deep sea. When the diver comes out, `N_2` bubbles out of blood causing pain. This diisease is Called, ‘bends’ In order to avoid this, `O_2` and He mixture is used.