Exp) Option b is the correct answer.

Statement I is incorrect: Rainforests do not produce more oxygen than oceans. The ocean, particularly through phytoplankton, is estimated to produce a significantly larger portion of Earth’s oxygen than land-based ecosystems like rainforests. While estimates vary, the ocean is thought to produce a substantial portion of the world’s oxygen, ranging from 50% to 80%, while land-based ecosystems like rainforests contribute around 28%

Statement II is correct: Marine phytoplankton are primarily responsible for a significant portion of Earth’s oxygen production, with estimates suggesting they produce between 50% and 80% of the oxygen in the atmosphere. Synthetic bacteria, while involved in oxygen production in some cases, are not the primary source of oxygen for the planet

Statement III is incorrect: The concentration of dissolved oxygen in surface water is much lower than the concentration of oxygen in air. Air contains about 21% oxygen by volume, which is significantly higher than dissolved oxygen levels in water (typically around 8–10 mg/L).

Source: https://oceanservice.noaa.gov/facts/ocean-oxygen.html#:~:text=About%20half%20of%20Earth’s%20oxygen,%2C%20temperature%2C%20and%20other%20factors.

https://onetreeplanted.org/blogs/stories/oxygen-tree

https://www.globalseafood.org/advocate/dissolved-oxygen-is-a-major-concern-in-aquaculture-heres-why/#:~:text=Water%20holds%20a%20much%20smaller,deplete%20the%20dissolved%20oxygen%20quickly.