The expected pattern for ionization potential is

$$\ce{Cu} > \ce{Ag} > \ce{Au},$$

but the observed patter or experimental value is

$$\ce{Au} > \ce{Cu} > \ce{Ag}.$$

What could be a justification for this?

The simple way to look upon is a general increase in size which fails here. So, I suspect introduction of f-orbital in gold has to do something with it which is absent in copper and silver.

  • $\begingroup$ Think about and search for possible answers thoroughly before posting a question to prevent writing up redundant information. Include what you already know/thought about, what you found in textbook or online resources, what you have understood or not/tried/failed. Written effort attracts elaborated answers. Questions without elaboration effort are not very welcome, and may be closed. $\endgroup$
    – Poutnik
    Dec 6, 2020 at 7:30
  • $\begingroup$ Poor nucleus shielding by f electrons, lanthanoid contraction and relativistic 6s orbital contraction may play the role. Compare the trend in in neighbor groups. $\endgroup$
    – Poutnik
    Dec 6, 2020 at 12:21
  • $\begingroup$ @Mithoron my question talks about ag also $\endgroup$
    – Anu Oberoi
    Dec 7, 2020 at 4:55