The magnetic moment (spin-only) of $[NiCl_4]^{2-}$ is ........ $B.M.$

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? $[Cr = 24, Mn = 25, Fe = 26, Co = 27]$

Which of the following is true for $[Fe(CN)_6]^{3-}$ and $[FeF_6]^{3-}$?

Which of the following will show optical isomerism?
$I$. $\text{Cis}-[Co(NH_3)_2(en)_2]^{3+}$
$II$. $\text{Trans}-[IrCl_2(C_2O_4)_2]^{3-}$
$III$. $[Rh(en)_3]^{3+}$
$IV$. $\text{Cis}-[Ir(H_2O)_3Cl_3]$

For a transition metal with a $d^7$ configuration,the magnetic susceptibility (magnetic moment) 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: