National League for Nursing (NLN PAX) Practice Exam

A synthesis reaction involves the combination of two or more reactants to form a single product. The best illustration of a synthesis reaction in this context is the equation where sodium (Na) and chlorine gas (Cl2) combine to form sodium chloride (NaCl). This reaction clearly shows two elements coming together to create a compound, which is the defining feature of a synthesis reaction.

In this specific reaction, two sodium atoms react with one molecule of chlorine gas (which consists of two chlorine atoms) to produce two formula units of sodium chloride. This type of reaction demonstrates the principle of combining simple substances to form a more complex compound, highlighting the essence of synthesis.

The other equations illustrate different types of reactions. For example, the equation involving water breaking down into hydrogen and oxygen represents a decomposition reaction, where a single compound breaks down into two or more products, rather than creating something new from simpler components.

Thus, the synthesis reaction is characterized by the formation of new substances from the combination of simpler ones, and the equation involving sodium and chlorine best exemplifies this principle.