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 photosynthetic 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?

Statement II is correct because marine phytoplankton and cyanobacteria contribute approximately 50% to 80% of Earth's oxygen through photosynthesis, significantly more than terrestrial ecosystems. Statement I is a common misconception; although rainforests are highly productive, the vast surface area and volume of the oceans make them the primary global oxygen source. Statement III is false because atmospheric air contains roughly 21% oxygen, whereas even well-oxygenated water holds only a tiny fraction of that amount, typically measured in milligrams per liter (ppm). The core concept tested is the global oxygen cycle and the comparative biological productivity of marine versus terrestrial biomes.