A homologous series is characterized by?

• A. Similar chemical properties and trends in physical properties; represented by a general formula
• B. Identical physical properties
• C. Different molecular formulas
• D. No shared properties

Answer: (A)

A homologous series is a family of organic compounds that all share the same functional group and differ from one member to the next by a CH2 unit. Because the reactive part is the same, their chemical behaviour is very similar, so they react in much the same way. As the chain length increases, their physical properties change in a regular, predictable way—boiling points and melting points tend to rise due to greater van der Waals forces, while other properties follow a orderly trend.

The pattern is captured by a general formula that describes all members of the series, showing the systematic way the formula changes with each added CH2 group (for example, many hydrocarbon series have formulas that increment by CH2 as n increases). This combination of similar chemistry and predictable physical trends, together with a general formula, is what uniquely characterizes a homologous series.