Question

The first element of rare-earth metal is?
(a)Cerium
(b)Actinium
(c)Uranium
(d)Lanthanum

Answer 1

Hint: The rare-earth elements are also known as rare-earth metals, rare earth-oxides, or the lanthanides. These are a set of $17$ elements which are indistinguishable and are lustrous and silvery-white soft heavy metals. The complete solution of this question is given in the below section in brief.

Complete answer:
Lanthanum is the first rare-earth metal. Therefore, option D is the correct option. There are two more metals which are considered to be rare-earth metals and they are scandium and yttrium because they are found in the same ore deposits where the lanthanides are found. They also exhibit the same chemical properties. The only difference comes in their electronic and magnetic properties. These metals react slowly with cold water to form hydroxides, liberating hydrogen. These metals also tarnish slowly in air at room temperature. They also react with steam and form oxides but at elevated temperature, they ignite spontaneously and burn with a fierce colorful pyrotechnic flame. The metals which are soluble in water are mildly to moderately toxic whereas the elements which are insoluble in water are not toxic in nature.
Hence the correct answer is option D.

Note:
These elements and their compounds do not play any role in the field of biological functioning. These rare-earth metals are mostly used as catalysts and magnets also. They are also used in ceramic, glass and polishing. Cerium and Lanthanum are used for petroleum refining and also as diesel additives. These elements are also used in the production of high performance magnets, alloys and electronics, etc.