The magnetic moment of a metal ion from the first transition series is $2.83 \, BM$. How many unpaired electrons are present in this ion?

The magnetic moment of ${K_3}[Fe(CN)_6]$ is found to be $1.7 \ B.M.$ How many unpaired electron$(s)$ is/are present per molecule?

Which among the following elements in their respective oxidation states develops the lowest spin-only magnetic moment? (Atomic numbers: $Cu=29, Fe=26, Ni=28, Co=27$)

The 'Spin only' magnetic moment for $[Ni(NH_3)_6]^{2+}$ is $ . . . . . . \times 10^{-1} \ BM$.
(Given: Atomic number of $Ni = 28$)

Of the following configurations,the optical isomers are

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