What is the magnetic moment (in $B.M.$) of ${K_3}[FeF_6]$?

Which of the following is paramagnetic?

Total number of unpaired electrons present in the central metal atoms/ions of $[Ni(CO)_{4}]$,$[NiCl_{4}]^{2-}$,$[PtCl_{2}(NH_{3})_{2}]$,$[Ni(CN)_{4}]^{2-}$ and $[Pt(CN)_{4}]^{2-}$ is . . . . . . .

The isomer$(s)$ of $[Co(NH_{3})_{4}Cl_{2}]^{+}$ that has/have a $Cl-Co-Cl$ angle of $90^{\circ}$ is/are:

The magnetic moment of $Ni^{2+}$ in an aqueous solution is ......... $B.M.$

On treatment of $[Ni(NH_3)_4]^{2+}$ with concentrated $HCl,$ two compounds $I$ and $II$ having the same formula,$Ni(NH_3)_2Cl_2$ are obtained. $I$ can be converted into $II$ by boiling with dilute $HCl.$ $A$ solution of $I$ reacts with oxalic acid to form $[Ni(NH_3)_2(C_2O_4)]$ whereas $II$ does not react. Point out the correct statement of the following: