Dissociation reactions occur when one molecule is divided to form two smaller ones, leading to a decrease in energy. Dissociation reactions result in the break down of a large molecule to form smaller products, giving them their second name: decomposition reactions.

Many decomposition reactions can also be classified as hydrolysis reactions, if water is used as a reactant. One example of this is the breakdown of glycogen to form glucose monomers. Dehydration reactions release water in order to form a new bond, building a larger molecule from smaller reactants (synthesis).

When one molecule is converted into two or more smaller molecules, the reaction is considered a decomposition reaction. In this example, none of the elements under go a change in oxidation number, so this is not an oxidation-reduction reaction. (Calcium is always , oxygen is always , and carbon remains throughout the reaction.)

Dissociation reactions usually entail a salt or ionic compounds dissociating or splitting into its components. In this case, where AB is made up of the components A and B. This reaction is ideally reversible even though the question does not provide the reversible arrows.

The options that include a third species, would be incorrect, as there are only two species in the original compound that is dissociating.