$[Co(NH_3)_5NO_2]Cl_2$ and $[Co(NH_3)_5(ONO)]Cl_2$ are related to each other as

Explain the magnetic properties of coordination compounds.

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:

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

Ordinary light is converted into plane-polarized light with the help of which of the following?

Which of the following complex compounds is optically inactive?