Solubility of iodine in water is greatly increased by the addition of iodide ions because of the formation of ......

In the following reaction sequence in aqueous solution,the species $X, Y$ and $Z$,respectively,are

$A$ solution containing $2.675 \ g$ of $CoCl_3 \cdot 6 NH_3$ (molar mass $= 267.5 \ g \ mol^{-1}$) is passed through a cation exchanger. The chloride ions obtained in solution were treated with excess of $AgNO_3$ to give $4.78 \ g$ of $AgCl$ (molar mass $= 143.5 \ g \ mol^{-1}$). The formula of the complex is
(At. mass of $Ag = 108 \ u$)

In ${K_4}[Fe(CN)_6]$,$Fe$ is in the form of

Assign $A, B, C, D$ from the given type of reaction:
$3KCN + Fe(CN)_3 \downarrow \longrightarrow K_3[Fe(CN)_6]$

Which of the following has the maximum ionic conductivity?