# The atomic numbers of the f-block elements are:

$\begin{array}{1 1}(a)\;58\;to\;71&(b)\;90\;to\;103\\(c)\;Both\;(a)\;and\;(b)&(d)\;None\end{array}$

58 to 71 and 90 to 103 (Lanthanides & actinides).
The group of 14 elements from Cerium(58) to Lutetium(71) are placed alongwith lanthanum in IIIB group and in the 6th period of the periodic table in a series below the periodic table called as Lanthanides.
The group of 14 elements from Thorium(90) to Lawrencium(103) are placed alongwith Actinum in IIIB group and in the 7th period of the periodic table in a series below the periodic table called as Actinides.
answered Jan 30, 2014
edited Oct 22