Name and characterize four main types of organic reactions: addition, substitution, elimination, and rearrangement.

• A. Addition moves electrons; Substitution eliminates bonds; Elimination adds functional groups; Rearrangement reduces oxidation state.
• B. Addition adds atoms to unsaturated bonds; Substitution replaces an atom/group; Elimination removes atoms forming a double or triple bond; Rearrangement reorganizes the carbon skeleton.
• C. Addition forms salts; Substitution hydrolyzes water; Elimination polymerizes; Rearrangement removes oxygen.
• D. Addition replaces atoms; Substitution forms multiple bonds; Elimination adds atoms; Rearrangement creates new functional groups.

Answer: (B)

Understanding how organic reactions are categorized by what happens to bonds and atoms helps you quickly identify and describe each type.

Addition involves adding atoms to unsaturated bonds (like carbon–carbon double or triple bonds), which saturates the bond. A classic example is hydrogenation of alkenes, where H atoms add across the double bond, turning it into an alkane.

Substitution is about replacing one atom or group with another. This is common at carbon centers where a leaving group is replaced by another nucleophile or reagent, such as halogen substitution on alkyl halides or substitution on aromatic rings.

Elimination is the reverse idea: atoms or groups are removed from a molecule to form a multiple bond, typically a double bond in alkenes or a triple bond in alkynes. This often accompanies the loss of a leaving group and a proton.

Rearrangement involves changing the connectivity of the carbon skeleton without changing the overall formula—atoms migrate within the molecule to give a more stable or otherwise different structure, such as hydride or alkyl shifts that relocate groups and generate a different carbocation or product.

The correct description above aligns with the idea that each type is defined by how bonds and atoms are altered. The other options mix up these actions (for example, saying addition moves electrons, or elimination polymerizes, or substitution forms multiple bonds), which aren’t accurate characterizations of these reaction classes.