Question

Identify the lanthanide which is obtained only by the synthesis:
(a) $Lu$
(b) $Pm$
(c) $\Pr$
(d) $Gd$

Answer 1

The lanthanide which is obtained only by synthesis has an atomic number $61$ . It is a radioactive element and all its isotopes are also radioactive. This element is generally used for research purposes. The period number of this element is $6$ . The block of this element is $f - block$ . It has no biological role.

Complete step-by-step answer: The lanthanide obtained only by the synthesis is Promethium $Pm$ .
So, the correct option for this question is option (b) $Pm$ .
Let’s see why other options are not right.
Option A is Lutetium, it is not the right option as:
$Lu$ (Lutetium) never occurs in nature as a free element. It is found in ores, monazite sand and bastnasite ores having a minute amount of all the rare earth metals. It is difficult to separate the particular lanthanide from other rare earth elements.
Option C is Praseodymium, it is not the right option as:
$\Pr$ (Praseodymium) is found along with other rare earth elements in a variety of minerals. Monazite and bastnasite are the two principal commercial sources of rare-earth metals.
Option D is Gadolinium, it is not the right option as:
$Gd$ (Gadolinium) is extracted from its oxide or salt by heating it with calcium in an argon atmosphere. Gadolinium in sponge form can be formed by reducing molten $GdC{l_3}$ with a suitable metal.

Note: Lanthanides are generally colored due to the presence of ions in the partially filled $f -$ orbitals. The lanthanides show a unique property known as lanthanide contraction in which there is the larger decrease in the ionic radii of the elements in the lanthanide series.