What type of reaction occurs when hydrochloric acid reacts with magnesium?

When hydrochloric acid reacts with magnesium, the reaction that takes place is an oxidation-reduction reaction, also known as a redox reaction. In this type of reaction, one substance gets oxidized while another gets reduced. In this specific reaction, magnesium loses electrons, which means it is oxidized, while the hydrogen ions (from hydrochloric acid) gain electrons, which means they are reduced to form hydrogen gas.

This reaction can be represented as follows:

[ \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \uparrow ]

Here, magnesium displaces hydrogen from hydrochloric acid, demonstrating the characteristic behavior of metals reacting with acids. The production of hydrogen gas is a clear indicator of the redox process occurring during the reaction.

Other types of reactions mentioned in the choices do not apply to this scenario. A neutralization reaction typically involves an acid reacting with a base to form water and a salt, while a combustion reaction involves the burning of a substance, usually in the presence of oxygen, leading to the release of energy, and a synthesis reaction involves two or more reactants combining to form a single product.