Question

The most common lanthanide is:
A.lanthanum
B.cerium
C.samarium
D.plutonium

Answer 1

Hint: Lanthanides are placed in the f-block of the periodic table. These lanthanide elements in the periodic table are called inner transition elements.

Complete step by step answer:
The most common lanthanide is cerium.
Atomic number of cerium is 58 and the electronic configuration of cerium is $\left[ {{\rm{Xe}}} \right]{\rm{4}}{{\rm{f}}^{\rm{1}}}{\rm{5}}{{\rm{d}}^{\rm{1}}}{\rm{6}}{{\rm{s}}^{\rm{2}}}$. Cerium is soft, iron grey-metal, ductile and malleable and it is very reactive. In cold water it oxidizes slowly and in hot water it oxidizes rapidly. Cerium tarnishes in the air readily and it can also burn if heated or if scratched with the help of a knife.

Hence option B is correct.

Additional information:
In the periodic table, the elements are placed in definite groups and periods. The elements placed in a group or in a period have similar chemical and physical properties. The chemical and physical properties follow a definite trend across the period and the group, such as electronegativity, atomic radii, ionization energy, metallic character, chemical reactivity, ionic radius etc. The periodic table includes four blocks. These are s-block, p-block, d-block and the f-block.
Lanthanides have the electronic configuration $\left[ {{\rm{Rn}}} \right]{\rm{5}}{{\rm{f}}^{{\rm{1}} - {\rm{14}}}}{\rm{6}}{{\rm{d}}^{{\rm{0}} - {\rm{1}}}}{\rm{7}}{{\rm{s}}^{\rm{2}}}$ and these Lanthanides are placed in the F-block of the periodic table. Lanthanoids have a total of 14 elements which are Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium and Lutetium. Lanthanoids are also termed as rare earth metals as well as inner transition metals. The lanthanides are silver-coloured metals and they are reactive.

Note:
It is important to note that, in the periodic table all the elements have an identifiable atomic number according to which they are placed in the periodic table. Each element has a definite chemical formula to express the chemicals present in the periodic table in the short form.