Carbon dioxide:

**The reasoning** Carbon dioxide is a **chemical compound** made of **one carbon atom (C) and two oxygen atoms (O₂)**. The subscript "₂" tells you there are *two* oxygen atoms bonded to the carbon. So the formula is **CO₂**. Think of it like this: "di-" means two (like "bicycle" has two wheels). Carbon *di*oxide = carbon + two oxygens = CO₂. **Why the wrong options tempt you** - **A) CO** — This is carbon *mon*oxide (one oxygen). Students confuse the names, but "monoxide" = one oxygen, "dioxide" = two oxygens. - **C) C** — This is just the element carbon by itself, not a compound with oxygen. - **D) CH₄** — This is methane (carbon + four hydrogens). It has nothing to do with oxygen, but students sometimes guess compounds randomly. **Quick takeaway** Remember: **Carbon dioxide = CO₂** (the "di" in dioxide means TWO oxygens). Names in chemistry directly tell you the formula! Master this pattern and you'll ace similar questions.