The highest oxidation state shown by transition elements is

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

Most stable cation in aqueous medium is

Which element from the following is a soft element?

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

Among the following series of transition metal ions,the one in which all the metal ions have $3d^2$ electronic configuration (excluding the $3p^6$ core) is (Atomic number: $Ti=22, V=23, Cr=24, Mn=25$)