Which one of the following has the highest molar conductivity?

Which compound is formed when an excess of $KCN$ is added to an aqueous solution of copper sulphate?

$A$ 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 $Ag = 108 \ u$)

The compound $ZnFe_2O_4$ is:

Nitrate is detected by the ring test. The brown color of the ring is due to which of the following?

When aqueous sodium hydroxide is added to an aqueous solution of chromium $(III)$ ions,a green-blue precipitate is first formed which re-dissolves to give a green solution. This green colour is due to