What is a homologous series in organic chemistry?

A homologous series is defined as a family of organic compounds that share the same functional group, which gives them similar chemical properties. In this series, each successive compound differs from the previous one by a specific structural unit, often a –CH₂– (methylene) group, leading to a predictable change in physical properties, such as boiling points and melting points. This consistency allows chemists to anticipate how compounds in that series will behave in reactions.

For instance, consider the alkane series (like methane, ethane, propane, etc.); all members contain single carbon-carbon bonds and the same functional group (saturated hydrocarbons) while differing in the number of carbon atoms. This structural similarity is key to understanding their reactivity and interactions.

The other options do not accurately describe what constitutes a homologous series in organic chemistry. A group of compounds with varying functional groups lacks the defining property of sharing a common functional group, while a collection of inorganic compounds does not fall under the category of homologous series, which specifically pertains to organic compounds. Lastly, a series of compounds produced by combustion does not define a homologous series, which focuses instead on the structural and chemical similarities among compounds within the same series.