Which of the following complexes will be optically inactive?

The complexes $[Co(NH_3)_5Br]SO_4$ and $[Co(NH_3)_5SO_4]Br$ can be distinguished by which of the following reagents?

The number of paramagnetic species from the following is $............$.
$[Ni(CN)_4]^{2-}, [Ni(CO)_4], [NiCl_4]^{2-}$
$[Fe(CN)_6]^{4-}, [Cu(NH_3)_4]^{2+}$
$[Fe(CN)_6]^{3-}$ and $[Fe(H_2O)_6]^{2+}$

If the magnetic moment of $[Ag(CN)_2]^{-1}$ is zero,then the number of unpaired electrons will be

The magnetic moments of the complexes given below are in the order:
$I. [Ni(CO)_4]$
$II. [Mn(CN)_6]^{4-}$
$III. [Cr(NH_3)_6]^{3+}$
$IV. [CoF_6]^{3-}$

What is the spin-only magnetic moment of an element having one unpaired electron (in $BM$)?