A knowledge of chemistry is not required to find the odd one out:
Hint: An atlas will serve you better than a chemistry textbook.
Highlight for answer: b) Gold. All the others are named after towns or regions--Ytterby, Sweden (also a source of Yttrium, Terbium, Erbium, Thulium (after Thule, the northernmost land in myth), Holmium (after Stockholm), Scandium (after Scandinavia); Ruthenium after the demographic area (never quite a nation) uncomfortably squeezed between Poland, Russia, Slovakia, and the Ukraine; Copper after Cyprus (it may be the other way 'round); and Lutetium after Lutetia, the Latin name for Paris. Other goodies include Strontium, named after a town in Scotland; Rhenium, after the Rhine; Hafnium, after the Latin for Copenhagen; Dubnium, after Dubna in Russia; and gimmes like Americium, Germanium, Europium, Polonium, Francium, Berkelium, Californium, Darmstadtium, and Livermorium.
I just noticed that last week's wordage was more or less a repeat of a much earlier one. My bad.