Write the formula of coordination compound mercury tetrathiocyanato-cobaltate (III):

Hint: We have to check if any number is written in the name of the complex to find the ligand. We have to see if there is any name mentioned at the end of the name to find the name of the metal. If there is any roman number written or not at the end of the IUPAC name.

Complete step by step solution:
-In the question, it is given that we have to write the chemical formula of mercury tetrathiocyanato-cobaltate (III) complex.
-In the name, there is a word cobaltate at the end of the name means in the given complex cobalt is the central metal atom that is in the form of the anion. Cobaltate the word ended with ate means cobalt is a part of the anion in the complex.
-Again it is mentioned as tetra thiocyanate, tetra means four, thiocyanate means SCN (ligand).
-In IUPAC name before the ligand the words tetra, penta, Hexa will be mentioned.
-The name of the complex is started with mercury means it is present in the cation part of the complex.
-At last of the name it is mentioned as III in brackets means it is the oxidation state of the central metal cobalt in the complex.
- By observing all the above points we can write the structure of the complex as follows.
\[Hg[Co{{(SCN)}_{4}}]\]

Note: The oxidation state of the cobalt in the above complex can be calculated as follows.
\[Hg[Co{{(SCN)}_{4}}]\to H{{g}^{+}}+{{[Co{{(SCN)}_{4}}]}^{-}}\]
- The complex will be dissociated in the water as above.
- Then
$x +$ $4(-1) =$ $-1$
$x =$ $-1 +4$
$x =$ $3$.
Here x = oxidation number of the cobalt.