Which of the following complex ions is the most stable?

Which among the following cations forms the most stable complex with the same ligand?

Which of the following coordination compounds acts as a non-electrolyte in solution?

When ammonia is added to a cupric salt solution,the deep blue colour is observed; it is due to the formation of

$A$ 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 $(Ag = 108 \ u)$:

Which of the following orders is correct in the spectrochemical series of ligands?