What type of isomerism is exhibited by $[Co(NH_3)_6][Cr(CN)_6]$ and $[Cr(NH_3)_6][Co(CN)_6]$?

$\mu = \sqrt{15}$ is true for the pair :-

What is the magnetic moment value of $Ni^{2+}$ in an aqueous solution in Bohr Magnetons? (Atomic number: $Ni = 28$)

The total number of unpaired electrons present in the complex $K_3[Cr(C_2O_4)_3]$ is ..........

Which one of the following compounds is not coloured?

Among $VO_2^{+}$,$MnO_4^{-}$ and $Cr_2O_7^{2-}$,the spin-only magnetic moment value of the species with least oxidising ability is $BM$ (Nearest integer). (Given atomic number $V=23$,$Mn=25$,$Cr=24$)