What do all the members of one homologous series share?

1. Adding one carbon atom to an alkane also adds two hydrogen atoms, so each member differs from the last in a fixed way. 2. A set of compounds built on that pattern is called a homologous series. 3. Every member of the series obeys the same general formula and carries the same functional group. 4. Molecular mass rises steadily along the series, so it cannot be the shared property. 5. Boiling point rises with chain length too, which rules out that option as well. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 4: Organic molecules_