Which complex compound is most stable?

For the reaction given below:
$CoCl_{3} \cdot xNH_{3} + AgNO_{3(aq)} \rightarrow$
If two equivalents of $AgCl$ precipitate out,then the value of $x$ will be $....$

The compounds containing complex oxyanion $CrO_4^{2-}$ are intensely yellow coloured because

What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes.

Assign $A, B, C, D$ for the type of observation in the following reaction:
$CuSO_4 + KCN \text{ (excess)} \longrightarrow K_3[Cu(CN)_4] + \frac{1}{2}(CN)_2$

$A$ pink coloured aqueous solution of $Co(NO_3)_2$ turns blue on the addition of $HCl$ gradually. This colour change happens due to the formation of