The thermodynamic stability of transition metal elements is based on which of the following?

Which pair of metal ions from the following has the same number of unpaired electrons?

Most transition metals exhibit several characteristic properties. Which of the following statements are correct?
$I$: Form sets of compounds which display different oxidation states of the metal.
$II$: Form coloured ions in solution.
$III$: Burn vigorously in oxygen.
$IV$: Act as catalysts.

Which among the following elements does $NOT$ exhibit ferromagnetic properties?

Ferrous ion changes to $X$ ion upon reacting with acidified hydrogen peroxide. The number of $d$-electrons present in $X$ and its magnetic moment (in $BM$) are,respectively:

Assertion: Transition metals and their complexes show catalytic activity.
Reason: The activation energy of a reaction is lowered by the catalyst.