Statement - I : Deep sea divers use helium-oxygen mixture for respiration
Statement - II : Unlike nitrogen, helium is not soluble in blood even under high pressure.

Statement I is true because deep sea divers use a mixture of helium and oxygen to prevent nitrogen narcosis and oxygen toxicity. At high pressures, nitrogen can dissolve in the body's tissues and cause narcosis, which can impair judgment and lead to dangerous situations. Meanwhile, oxygen toxicity can cause seizures and other serious health problems. By using a helium-oxygen mixture, divers can avoid these issues.

Statement II is also true because helium is much less soluble in blood than nitrogen, even under high pressure. This means that as divers descend to greater depths, the helium in their breathing mixture is not absorbed into their bloodstream and tissues to the same extent as nitrogen would be. This helps to prevent nitrogen narcosis and other health problems associated with high-pressure environments.