I would like to use the word serial in the sense that it denotes a sequential arrangement of objects. In that regard, is it better to say “serial potential drop” instead of “a series of potential drops”?
If you are speaking of a set of voltage drops across resistors arranged in series, use the latter phrasing: “a series of potential drops” or perhaps better, “a series of voltage drops”. “Serial potential drop” probably is technically ok, ie is not wrong, but because of being rarely used may jar the reader. However, if you want to emphasize that there is a descending scale of voltages along a resistor chain, as found for example in 256-resistor or 1024-resistor flash ADC parts, serial potential drop might be an appropriate phrase to use.