Magnetic moment is expressed in

Which of the following ions are diamagnetic ?

The 'spin only' magnetic moment value of $\mathrm{MO}_4{ }^{2-}$ is . . . . . BM. (Where $\mathrm{M}$ is a metal having least metallic radii. among $\mathrm{Sc}, \mathrm{Ti}, \mathrm{V}, \mathrm{Cr}, \mathrm{Mn}$ and $\mathrm{Zn}$ ).

(Given atomic number: $\mathrm{Sc}=21, \mathrm{Ti}=22, \mathrm{~V}=23$, $\mathrm{Cr}=24, \mathrm{Mn}=25$ and $\mathrm{Zn}=30)$

For the following Assertion and Reason, the correct option is

Assertion : For hydrogenation reactions, the catalytic activity increases from Group $5$ to Group $11$ metals with maximum activity shown by Group $7-9$ elements.

Reason : The reactants are most strongly adsorbed on group $7-9 $ elements.

The ability to form complex compounds by the transitional metal ion is due to

Which have melting point below $500\,^{\circ} C$.