Which gas is produced when acid reacts with a metal?

## The reasoning When an acid reacts with a metal, the metal displaces hydrogen from the acid. This is a **single displacement reaction**. The general equation is: **Metal + Acid → Salt + Hydrogen gas** For example: - Zn + H₂SO₄ → ZnSO₄ + H₂↑ - Mg + 2HCl → MgCl₂ + H₂↑ The hydrogen atoms in the acid (H⁺ ions) gain electrons from the metal and form H₂ gas, which bubbles out. You can test this gas by bringing a burning splint near it — it produces a "pop" sound (that's your laboratory test for hydrogen!). ## Why the wrong options tempt you **Oxygen** comes from decomposition of compounds like water or metal oxides with heat — not from acid-metal reactions. **Carbon dioxide** is produced when acids react with *carbonates or bicarbonates* (like limestone), not pure metals. **Nitrogen** isn't typically released in simple acid-metal reactions at all. ## Quick takeaway **"Acid eats metal, spits out hydrogen"** — remember this, and you'll never confuse it with carbonate reactions (which give CO₂).