Chemistry - Complete d-block Question with Solution | TestHub

The d-block elements are distributed into four transition series based on the filling of d-orbitals:

First transition series ($3d$ series): Sc ($Z=21$) to Zn ($Z=30$)

Second transition series ($4d$ series): Y ($Z=39$) to Cd ($Z=48$)

Third transition series ($5d$ series): La ($Z=57$), Hf ($Z=72$) to Hg ($Z=80$)

Fourth transition series ($6d$ series): Ac ($Z=89$), Rf ($Z=104$) to Cn ($Z=112$)

Therefore, there are a total of $4$ transition series of d-block elements.

Answer: $4$