Answer:
The correct answer is A. Double-Displacement
Explanation:
A double displacement reaction is that two elements found in different compounds exchange positions, forming two new compounds. These chemical reactions do not present changes in the number of oxidation or relative load of the element. Generally the exchange occurs between reagents that are ionic compounds in solution, where the anions and cations of the compounds are exchanged.
Double displacement reactions follow the following general chemical equation:
AB + CD --- AD + CB
The initial compounds AB and CD react by exchanging "their partners" and thus form two new compounds: AD and CB. This reaction takes place if and only if A and D are more similar than A and C, or if CB links are more stable than those of CD. Since the reaction is a simple ion exchange, none of these gain or lose electrons, as mentioned above. Thus, if A is a +1 charge cation in compound AB, it will have the same +1 charge in compound AD.
The solvent of the double displacement reactions is almost always water and the reagents and products are usually ionic compounds, although they can also be acids or bases.
On the other hand, a precipitation reaction occurs when two aqueous ionic compounds form a new ionic compound that is not soluble in water. It is an example of double displacement reactions. In most precipitation reactions, one salt is soluble and the other precipitates. The insoluble compound that results is called precipitate. The solvent and soluble reaction compounds are called the supernatant. This is the type of reaction that happens in this case. In this case the insoluble compound is cadmium sulfide CdS.
