$[Cu(CN)_4]^{2-}$ is colourless as it absorbs light in

Aqueous copper sulphate solution (blue in colour) gives:
$(i)$ a green precipitate with aqueous potassium fluoride,and
$(ii)$ a bright green solution with aqueous potassium chloride
Explain these experimental results.

The formula of the complex formed in the ring test for $NO_2^-$ and $NO_3^-$ is .....

The active substance in Nessler's reagent used for the detection of ammonia 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 $(Ag = 108 \ u)$:

Identify the complex with the maximum conductivity.