Which type of reaction involves the formation of chemical bonds?

The formation of chemical bonds is characteristic of anabolic reactions. Anabolic reactions are metabolic pathways that construct larger molecules from smaller units, which requires energy input. These processes build complex molecules, such as proteins and nucleic acids, from simpler substrates, and during this process, new chemical bonds are formed.

For example, in protein synthesis, amino acids are linked together by peptide bonds to form proteins, which is a clear demonstration of an anabolic reaction at work. These reactions are essential for growth, repair, and maintenance of tissues in living organisms.

In contrast, exothermic reactions typically involve the release of energy, catabolic reactions break down larger molecules into smaller ones (which involves the breaking of bonds rather than forming them), and reduction reactions refer specifically to the gain of electrons by an atom or molecule, which can involve bond alterations but doesn't necessarily mean new bonds are being formed. Therefore, the defining characteristic of anabolic reactions is their role in creating new chemical bonds, making it the correct answer for this question.