Detailed Explanation:

Correct Answer: ✅ Option 2 (II only)

Most people associate oxygen production with forests, but the oceans are actually the largest source of Earth's oxygen. Marine phytoplankton, algae, and photosynthetic bacteria contribute roughly half of the global oxygen production. Also, atmospheric air contains much higher oxygen concentrations than water.

❌ Statement I is Incorrect: Oceans produce more oxygen than rainforests. Marine phytoplankton are responsible for a major share of global oxygen production.

✅ Statement II is Correct: Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen through photosynthesis.

❌ Statement III is Incorrect: Atmospheric air contains about 21% oxygen, whereas even well-oxygenated water contains only a small amount of dissolved oxygen. Water does not contain several times more oxygen than air.

Short Notes: Oxygen Cycle and Marine Phytoplankton

• Marine phytoplankton produce nearly 50% of Earth's oxygen.

• Phytoplankton are microscopic photosynthetic organisms found in oceans.

• Oceans are the largest contributor to global oxygen production.

• Atmospheric air contains about 21% oxygen.

• Dissolved oxygen in water is usually measured in mg/L, much lower than oxygen concentration in air.

• Photosynthesis converts CO₂ + Water → Glucose + Oxygen.

• Healthy oceans are essential for maintaining Earth's oxygen balance and climate system.