What is the formula of ferric ferrocyanide?

Which of the following metal ions forms a complex with $CN^-$ having a coordination number of $2$?

Mohr's salt is

$2.33 \ g$ of compound $X$ (empirical formula $= CoH_{12}N_{4}Cl_{3}$) upon treatment with excess $AgNO_{3}$ solution produces $1.435 \ g$ of a white precipitate. The primary and secondary valences of cobalt in compound $X$,respectively are.
[Given,atomic mass : $Co = 59, Cl = 35.5, Ag = 108$]

On the basis of the following observations made with aqueous solutions,assign secondary valences to metals in the following compounds:

Formula	Moles of $AgCl$ precipitated per mole of the compound with excess $AgNO_3$
$(i) PdCl_2 \cdot 4NH_3$	$2$
$(ii) NiCl_2 \cdot 6H_2O$	$2$
$(iii) PtCl_4 \cdot 2HCl$	$0$
$(iv) CoCl_3 \cdot 4NH_3$	$1$
$(v) PtCl_2 \cdot 2NH_3$	$0$

Which of the following complexes is not a chelate complex?