The term ‘rare earths’ is in fact a , .............. for paradoxically, the rare-earth elements are in actuality ............., being presentin low concentration in virtually all the minerals.

The sentence talks about the term "rare earths" and how it's not quite accurate because these elements are actually quite common, not rare.

"Misnomer" means a wrong or inaccurate name, which fits perfectly because "rare earths" is not the right term. "Ubiquitous" means something that is found everywhere, which fits because these elements are present in many minerals, just in small amounts.

So, the correct choice is Misnomer — ubiquitous, meaning the term is wrong because these elements are actually found everywhere.