Thanks for both your help. Weecalf can you explain you’re answer. I thought of Montevideo, or Brazzaville, but I don’t get the two atomic numbers part.
Yes NAC - my original answer also crossed with yours, you were not thinking of Zinc - But I was
But then I realised that zinc was Zn and so looked up "atomic number" to find like you say it is the symbol for the "atomic number"
Thank you everybody for your suggestions. I thought it must be Brazzaville but couldn’t get the atomic number part. Thanks jj109 for explanation, much appreciated.
Thanks Neveracrossword for your invaluable help. Would have put you as best answer, but pressed wrong button. Must be due to too much Christmas cheer! Happy New Year to all.