With reference to the planet Earth, consider the following statements: I. Rain forests produce more oxygen than that produced by oceans. II. Marine phytoplankton and photo-synthetic bacteria produce about 50% of world's oxygen. III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air. Which of the statements given above is/are correct?

I. Incorrect. Oceans are the major source of Earth’s oxygen; marine photosynthesizers contribute roughly half of global oxygen, so rain forests do not produce more than oceans.

II. Correct. Marine phytoplankton and photosynthetic bacteria are estimated to produce about 50% of the world’s oxygen.

III. Incorrect. Atmospheric air has about 21% oxygen by volume, while even well-oxygenated surface water contains only dissolved oxygen in mg/L, far lower than air; water does not contain several-fold higher oxygen than the atmosphere.

Therefore, only statement II is correct.