Which one of the following metal complexes is most stable?

In which one of the following pairs of ions is there an ion that forms a coordination compound with both aqueous sodium hydroxide and ammonia,and another ion that forms a coordination compound only with aqueous sodium hydroxide?

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

Violet colour of $[Ti(H_2O)_6]Cl_3$ on heating changes to $........$

What is the color of a cobalt chloride solution?

Which of the following complexes represents maximum stability?