Number of ions present in $K_4[Fe(CN)_6]$

Give the chemical formulas for the following:
$(i)$ Sodium nitroprusside
$(ii)$ The purple solution formed in the test for sulphur
$(iii)$ Sodium hexacyanoferrate $(II)$
$(iv)$ Iron $(III)$ hexacyanoferrate $(II)$
$(v)$ Ferri-ferrocyanide
$(vi)$ Sodium thiocyanate

What is the total number of ligands bonded to a central metal ion by coordinate (sigma) bonds called?

The molecular formula of a coordination complex is $CoH_{12}O_6Cl_3$. When one mole of this aqueous solution of the complex is reacted with an excess of aqueous $AgNO_3$ solution,$3$ moles of $AgCl$ are formed. What is the correct formula of the complex?

The secondary valency of platinum in tetra-amminedichloroplatinum$(IV)$ chloride is

Identify the neutral ligand from the following.