Which gas do plants release during photosynthesis?

**The reasoning** During photosynthesis, plants use sunlight energy to convert carbon dioxide (CO₂) and water (H₂O) into glucose (food) and oxygen (O₂). The simplified equation is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ Notice what happens: plants **take in** carbon dioxide and **release** oxygen as a waste product. This oxygen is what we breathe! Think of it this way: plants do the opposite of what we do—we breathe in oxygen and breathe out carbon dioxide; they take in carbon dioxide and release oxygen. **Why the wrong options tempt you** **A) Carbon dioxide** — This is what plants *absorb*, not release. Easy mix-up if you remember the gases involved but forget which direction they move. **B) Nitrogen** — Plants need nitrogen for growth, but it comes from soil (as nitrates), not from photosynthesis. **D) Hydrogen** — Hydrogen is part of water molecules used in photosynthesis, but it's not released as a gas—it becomes part of glucose. **Quick takeaway** Plants breathe *opposite* to us: they take in CO₂, give out O₂—that's why forests are called "the lungs of the Earth."