Which gas is usually released when an acid reacts with a metal?

When an acid reacts with a metal, a chemical reaction occurs that usually produces hydrogen gas. This is a common reaction studied in chemistry, particularly in inorganic chemistry and acid-metal reactions. The general reaction can be written as:

Metal + Acid → Salt + Hydrogen gas

For example, when zinc reacts with hydrochloric acid, the reaction produces zinc chloride and hydrogen gas:

Zn + 2HCl → ZnCl₂ + H₂↑

Hydrogen gas is a colorless, odorless, and highly flammable gas. It is always released when reactive metals such as zinc, magnesium, or iron react with acids like hydrochloric acid (HCl) or sulfuric acid (H₂SO₄). The reaction occurs because the metal atoms lose electrons to the hydrogen ions (H⁺) from the acid, forming hydrogen gas.

Other options in the MCQ are not correct in this context:

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  Ammonia gas (NH₃) is released in reactions involving ammonium compounds with bases, not acids with metals.

  
  


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  Chlorine (Cl₂) is a halogen and is not produced in typical acid-metal reactions.

  
  


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  Oxygen (O₂) is a component of oxidation reactions but not released in standard acid-metal reactions.

  
  

Understanding this reaction is important because it demonstrates the reactivity of metals, the behavior of acids, and the concept of electron transfer in chemical reactions. It also explains why some reactions produce bubbles or effervescence, which is an observable property of hydrogen gas being released.

Hydrogen gas production from acid-metal reactions is a classic example in chemistry experiments and illustrates metal displacement reactions, activity series of metals, and the principles of redox reactions.