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

Which of the following complexes exhibits both geometrical and optical isomerism? $(en = \text{ethylenediamine})$

The total number of possible isomers of the complex compound $[Cu(NH_3)_4] [PtCl_4]$ is:

Which of the following predictions is correct when a transition metal ion is colourless?

In which of the following orders are the given complex ions arranged correctly with respect to their decreasing spin-only magnetic moment?
$(i)$ $[FeF_{6}]^{3-}$
$(ii)$ $[Co(NH_{3})_{6}]^{3+}$
$(iii)$ $[NiCl_{4}]^{2-}$
$(iv)$ $[Cu(NH_{3})_{4}]^{2+}$

The magnetic moment of a transition element is $\sqrt{15} \, B.M.$ Determine the number of unpaired electrons present in it.