The type of isomerism between $[Co(en)_2(NCS)_2]Cl$ and $[Co(en)_2(NCS)Cl]NCS$ is ............ .

The $d$ electron configurations of $Cr^{2+}, Mn^{2+}, Fe^{2+}$ and $Ni^{2+}$ are $3d^4, 3d^5, 3d^6$ and $3d^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?
(At. No. $Cr = 24, Mn = 25, Fe = 26, Ni = 28$)

Which of the following statements is not correct?

Which isomer of $CrCl_3 \cdot 6H_2O$ is green in color and reacts with $AgNO_3$ to form one mole of $AgCl$?

Which of the following complexes exhibit geometrical isomerism?
$I$) $[Co(en)(NH_3)_2 Cl_2] Cl$
$II$) $[Co(NH_3)_4 Cl_2] Cl$
$III$) $[Co(en)_3] Cl_3$
$IV$) $[Co(en)_2 Cl_2] Br$

Calculate the magnetic moment of a divalent ion in aqueous solution if its atomic number is $25$. (in $BM$)