What is formed when metal reacts with acid to liberate gas?

Analyze the question: A metal reacts with an acid and a gas is liberated. The question asks what is formed (besides the gas).

Concept: Reactive metals (those above hydrogen in the reactivity series, such as Mg, Zn, Fe, Al) react with dilute acids to produce a salt and hydrogen gas.

General equation:

Metal + Acid → Salt + Hydrogen gas

Worked examples:

• Zn + 2HCl → ZnCl₂ + H₂↑ (zinc chloride is the salt)
• Mg + H₂SO₄ → MgSO₄ + H₂↑ (magnesium sulphate is the salt)

Checking the options:

• A. Salt: Correct. Every metal-acid reaction of this type forms a salt along with hydrogen.
• B. Base: Wrong. Bases or alkalis are not products of this reaction. Metals react with water or steam to give hydroxides or oxides, but not with acids.
• C. Acid: Wrong. The acid is a reactant, and it gets used up.
• D. Liquid: Too vague. Water is not the main product here, and "liquid" is not a chemical class of product.

Salt**.

Exam tip: Remember "MASH": Metal + Acid → Salt + Hydrogen. The gas that "pops" with a lighted splint is hydrogen. Don't forget that unreactive metals like copper, silver and gold do not react with dilute acids this way.