Which from the following is a correct stability order of complexes formed by metal ions if the ligand remains the same?

When $Co(II)$ chloride is dissolved in concentrated $HCl$,a blue solution is obtained. Upon dilution with water,the colour changes to pink because:

For the complex $ML_2$,the stepwise formation constants for the reactions:
$M + L \rightleftharpoons ML$
$ML + L \rightleftharpoons ML_2$
are $4$ and $3$ respectively. Hence,the overall stability constant for the reaction:
$M + 2L \rightleftharpoons ML_2$
is:

Match List-$I$ (Molar Conductivity) with List-$II$ (Complex Formula) and select the correct option:

List-$I$ (Conductivity)	List-$II$ (Formula)
$A. \ 229$	$i. \ [Pt(NH_3)_3Cl_3]Cl$
$B. \ 97$	$ii. \ [Pt(NH_3)_4Cl_2]Cl_2$
$C. \ 404$	$iii. \ [Pt(NH_3)_5Cl]Cl_3$
$D. \ 523$	$iv. \ [Pt(NH_3)_6]Cl_4$

Which of the following has the highest molar conductivity in solution?

The aqueous solution of a transition metal salt changes colour from pink to blue when concentrated hydrochloric acid is added to it. The change in colour is due to: