In a substitution reaction, what happens to the groups on the carbon chain?

In a substitution reaction, one group on a carbon chain is replaced by another group on the same carbon atom. This process involves the breaking of a bond between the original group and carbon, followed by the formation of a new bond between the carbon and the incoming group.

This means the product will still have the same number of atoms and maintain its overall structure, but with a different substituent attached. For example, if a chlorine atom is replaced by a hydroxyl group on a carbon chain, the identity of that carbon's substituent changes, but the fundamental carbon structure remains intact.

This contrasts with the other options. Adding two groups to the same carbon implies a different type of reaction, such as an addition reaction. Bonding two neighboring carbon atoms describes a different chemical transformation, typically associated with polymerization or formation of branched structures. Finally, removing atoms to create a double bond represents an elimination reaction. Therefore, option B captures the essential nature of a substitution reaction accurately.