Which of the following statements is $NOT$ consistent with the ability of transition metal ions to form complex compounds?

Which of the following does not react with $AgCl$?

$5.33 \text{ g}$ of $CrCl_3 \cdot 6H_2O$,which is a $1:3$ electrolyte,is dissolved in water and passed through a cation exchanger. The chloride ions in the eluted solution,on treatment with $AgNO_3$,result in $8.61 \text{ g}$ of $AgCl$. The ratio of moles of complex reacted and moles of $AgCl$ formed is . . . . . . $\times 10^{-2}$. (Nearest integer) [Molar mass in $\text{g mol}^{-1}$: $Cr = 52, Ag = 108, Cl = 35.5, H = 1, O = 16$]

The most stable ion is

Ammonia forms the complex ion $[Cu(NH_3)_4]^{2+}$ with copper ions in alkaline solutions but not in acidic solution. What is the reason for it?

The most stable complex among the following is