Calhn ingold prelog rules?

Is in in order of atomic mass or atomic number ?

Is it in order of atomic mass or atomic number ?

Whilst the choice between atomic number vs. atomic mass is unlikely to be of any consequence in assigning priority the original CIP rules are based on assigning priority to the highest atomic number. If atomic numbers are the same then the higher isotopic mass takes priority. If you get an exam question that asks how priority is assigned you should say by atomic number. I wrote to OCR to check how they want assignments to be made. Answer - atomic number.