The atomic radii of the elements are almost the same for which series?

Number of unpaired electrons in $Mn^{4+}$ is

The transition metals are mostly

Transition elements are more metallic than representative elements ($s-$ and $p-$ block elements) due to

How many of the following lanthanide elements exhibit $+4$ oxidation state?
$Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy$

Determine whether the following statements are True $(T)$ or False $(F)$:
$(a)$ The atomic radii of the elements of the second transition series $(4d)$ are larger than those of the first transition series $(3d)$.
$(b)$ $Cr^{+}$,$Mn^{2+}$,and $Fe^{3+}$ have the same electronic configuration.
$(c)$ $Cr^{+}$,$Mn^{2+}$,and $Fe^{3+}$ have the same $d^5$ electronic configuration.