In an octahedral complex $[Mabcdef]$,the total number of theoretical isomers 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 complexes will exhibit optical isomerism?

How many geometrical isomers are possible in the following coordination entities?
$(i)$ $[Cr(C_2O_4)_3]^{3-}$
$(ii)$ $[Co(NH_3)_3Cl_3]$

In the coordination complex $[CoF_6]^{3-}$,the number of unpaired electrons is equal to ......

The type of magnetism exhibited by $[Mn(H_2O)_6]^{2+}$ ion is