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

The correct order of magnetic moments (spin-only values in $B.M.$) among the following is:
(Atomic numbers: $Mn = 25, Fe = 26, Co = 27$)

Which one of the following is expected to exhibit optical isomerism $(en = \text{ethylenediamine})$?

The species with spin only magnetic moment of $\sqrt{24} \, BM$ is

The calculated spin-only magnetic moments of $[Cr(NH_3)_6]^{3+}$ and $[CuF_6]^{3-}$ in $BM$,respectively,are (Atomic numbers of $Cr$ and $Cu$ are $24$ and $29$,respectively).

Which one of the following has an optical isomer?
$(en = \text{ethylenediamine})$