Question

How many transition elements are there?

Answer 1

Hint: Periodic table in chemistry consists of s p d and block elements. Out of them the d block elements are termed as transition elements. The d block elements of the periodic table contain the elements of group $$3-12$$ in which the d orbitals are progressively filled in each of the four long periods. s block elements are metals, p block elements are non- metals but d block elements consist of metals, nonmetals and metalloids. Since they act as a transition state for change from metallic to non-metallic character, they are termed as transition elements.

Complete step-by-step answer:A transition element is defined as the one which has incompletely filled d orbitals in its ground state or in the most common oxidation state. The study of transition elements and their compounds is different from that of the main group elements because of the presence of partly filled d orbitals in their atoms. The d orbitals of the transition element project to the periphery of an atom more than the other orbitals (s and p).
In a periodic table, transition elements are distributed from $$3d$$ series to $6d$ series as shown below:
$3d$series

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

$4d$series

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

$5d$series

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

$6d$series

Rf

Db

Sg

Bh

Hs

Mt

Ds

Rg

Uub

$Zn,Cd,Hg$ are not typical transition elements because they have full $d^{10}$ configuration in their ground state as well as in their common oxidation state. However, being the last members of three transition series, their chemistry is studied along with them. Hence there are a total thirty-eight $\left(38\right)$transition elements in the periodic table.
Note: Always remember that zinc, cadmium and mercury are not typical transition elements, but they are just studied with the other transition elements. Also transition elements do not show a regular trend in their properties, their properties fluctuate regularly.