Hydrochloric acid is added to a beaker containing a piece of zinc. Zinc chloride is formed and hydrogen gas is released. This is an example of:

In this scenario, hydrochloric acid is reacting with zinc to form zinc chloride and release hydrogen gas. This is an example of a chemical reaction known as a single displacement reaction or a redox reaction. Here are the step-by-step details of the reaction:

1. Hydrochloric acid (HCl) is added to a beaker containing a piece of zinc (Zn).
2. The hydrochloric acid dissociates into hydrogen ions (H+) and chloride ions (Cl-). HCl → H+ + Cl-
3. The zinc metal reacts with the hydrogen ions from the hydrochloric acid. Zn + 2H+ → Zn2+ + H2
4. As a result of the reaction, zinc chloride (ZnCl2) is formed.
5. Simultaneously, hydrogen gas (H2) is released as a product of the reaction.
6. The overall balanced chemical equation for this reaction is: Zn + 2HCl → ZnCl2 + H2

So, the addition of hydrochloric acid to the beaker containing zinc, resulting in the formation of zinc chloride and the release of hydrogen gas, is an example of a single displacement or redox reaction.