Oxygen can be formed in several ways, depending on whether we’re talking about natural processes in the universe, Earth’s biosphere, or chemical reactions. Here are the main ones:
1. In Stars (Cosmic Formation)**
* Oxygen atoms are created in the cores of massive stars through **stellar nucleosynthesis**.
* Inside these stars, lighter elements like helium fuse under immense pressure and temperature to form heavier elements.
* When stars go supernova, they scatter oxygen (and other elements) into space, enriching the interstellar medium.
* That’s why oxygen is one of the most abundant elements in the universe.
2. On Earth – Biological Production**
* Most of the oxygen we breathe (O₂ gas) is produced by **photosynthesis**.
* Plants, algae, and cyanobacteria take in carbon dioxide (CO₂) and water (H₂O), and using sunlight, they produce glucose and release oxygen:
6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂
* Roughly **70–80% of Earth’s oxygen** comes from microscopic marine organisms (phytoplankton) in the oceans, not just trees.
3. Chemical Reactions**
Oxygen gas can also be formed in labs or naturally through:
* **Decomposition of hydrogen peroxide (H₂O₂):**
2H₂O₂ → 2H₂O + O₂
* **Thermal decomposition of certain salts (like potassium chlorate, KClO₃):**
2KClO₃ → 2KCl + 3O₂
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