The ratio of $cis$ and $trans$-isomers of the complex $[Ma_2bcde]^{n \pm}$ is

If the bidentate ligand ethane-$1, 2$-diamine $(en)$ is progressively added to a green aqueous solution of $[Ni(H_2O)_6]Cl_2$ in the molar ratios $en : Ni$ as $1 : 1, 2 : 1, 3 : 1$,then their associated spin-only magnetic moments (in $B.M.$ unit) are respectively

The electronic configurations of $Cr^{2+}, Mn^{2+}, Fe^{2+},$ and $Co^{2+}$ are $d^4, d^5, d^6,$ and $d^7$ respectively. Which of the following has the lowest magnetic moment? $[Cr = 24, Mn = 25, Fe = 26, Co = 27]$

The pair of metal ions that can give a spin-only magnetic moment of $3.9 \, BM$ for the complex $[M(H_2O)_6]Cl_2$ is

The magnetic moment of the central metal ion in $K_2MnO_4$ is ........ $B.M.$

Which of the following is paramagnetic?