Which of the following is the most stable complex ion?

Nitrate is confirmed by the ring test. The brown color of the ring is due to the formation of:

Copper sulphate solution reacts with $KCN$ to give

The aqueous solution of which of the following complexes has the least conductivity under identical conditions?

The conductivity measurement of a coordination compound of cobalt$(III)$ shows that it dissociates into $3$ ions in solution. The compound is

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