Step 1: The correct IUPAC name reflects the oxidation state of mercury (II) and the coordination of four thiocyanate ions.
Thus, the correct name is Mercury (II) tetrathiocyanato-S-cobaltate (II).
Consider the following complexes:
(A) [Co(CN)$_6$]$^{3-}$
(B) [Co(NH$_3$)$_5$H$_2$O]$^{3+}$
(C) [Co(H$_2$O)$_6$]$^{3+}$
(D) [CoF$_6$]$^{3-}$
The wavelength absorbed by the above complexes are in the order: