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UPSC PYQPrelims 2025

Civil Services Examination · Question 20

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?

  1. I and II
  2. II only
  3. I and III
  4. None of the above statements is correct
Show answer & explanation

Answer: (B) II only

Explanation

Oceans (via phytoplankton/bacteria) produce roughly half of Earth's oxygen — more than rainforests; dissolved oxygen in water is actually far lower in concentration than in air.