I know
that the rare earth elements (rare
earths) - a group of 17 elements consisting of lanthanum, scandium, yttrium and
the lanthanides. All these elements - metals silver-white color, while all have
similar chemical properties (most common in oxidation state +3). The name
"rare earth" is defined in connection with the fact that they are,
first, relatively rare in the crust (the content of (1.6-1.7) x 10-2% by
weight) and, secondly, to form a refractory substantially water-insoluble
oxides (oxides of these at the beginning of the XIX century and formerly known
as "lands").
That is why the correct answer is D)
