AQA GCSE Chemistry Paper 2 Practice Exam 2026 – Complete Study Resource

Compounds in a homologous series share the same general formula, which is a defining characteristic of such series. This means that each compound in the series differs from the next by a consistent increment, often a specific number of carbon and hydrogen atoms. For instance, alkanes, which are saturated hydrocarbons, have the general formula CnH2n+2, where 'n' represents the number of carbon atoms. This consistency in formula allows for predictions about the properties and behaviors of the compounds as one moves along the series.

In contrast to the other options, which suggest variability or a lack of shared characteristics, the statement that all compounds in a homologous series have different chemical formulas is misleading as they follow a clear pattern. Furthermore, claiming that only the carbon-hydrogen ratios are the same oversimplifies the concept, as the entire formula, including added functional groups or other elements, remains consistent throughout the series. Thus, the correct answer emphasizes the shared structure that defines the homologous series, enhancing our understanding of organic chemistry.