Which compound is formed when an excess of $KCN$ is added to an aqueous solution of copper sulphate?

Which of the following factors tends to increase the stability of metal ion complexes?

An aqueous pink solution of Cobalt $(II)$ chloride changes to deep blue on addition of excess of $HCl$. This is because:

Which among the following is a correct decreasing order of thermodynamic stability of the complexes?

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 stepwise stability constants of a complex are given below. What is its overall reaction stability constant $\beta_4$ ?
$M + L \rightleftharpoons ML ; K_1 = 1.0 \times 10^4$
$ML + L \rightleftharpoons ML_2 ; K_2 = 1.0 \times 10^3$
$ML_2 + L \rightleftharpoons ML_3 ; K_3 = 1.0 \times 10^3$
$ML_3 + L \rightleftharpoons ML_4 ; K_4 = 1.0 \times 10^2$
(Overall reaction : $M + 4L \rightleftharpoons ML_4$)