When an acid reacts with a metal, which one of the following gas is usually liberated?

A. Ammonia Gas
B. Chlorine
C. Oxygen
D. Hydrogen gas

 
When metal reacts with acid, a soap bubble is formed and the bubble contains Hydrogen gas (example: HCl, H2SO4).
Hydrogen gas is liberated when anacid reacts with a metal. For example, when zin cmetal reacts with dil. hydrogen is evolved and salt zinc chloride is formed as: It can be tested bybringing a burning candle near thegas.