Transition metals and their compounds act as catalysts because:

Which of the following series of transition metal ions has a $3d^2$ electronic configuration?

Observe the following statements:
$a$) The basic strength of $Lu(OH)_3$,$Gd(OH)_3$ and $Ce(OH)_3$ follows the order: $Ce(OH)_3 > Gd(OH)_3 > Lu(OH)_3$
$b$) $O^{2-}$,$N^{3-}$,$F^{-}$ and $Na^{+}$ are isoelectronic species
$c$) The sizes of $Zr$ and $Hf$ are approximately the same
The correct statements are:

Which one of the following is not a transition metal?

Which one of the following sets correctly represents the increase in the paramagnetic property of the ions?

The electrode potential of $M^{2+} / M$ for $3d$-series elements shows a positive value for which of the following?