Identify the lowest field strength ligand from the following.

Which of the following ions forms the most stable complex compound?

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:

Assign $A, B, C, D$ from the given type of reaction.
$Cr(OH)_3 \downarrow + NH_3 \text{ (excess)} \longrightarrow [Cr(NH_3)_6]^{3+}$

When concentrated $HCl$ is added to an aqueous solution of $CoCl_2$,its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?

$CuSO_4$ reacts with $KCN$ solution and forms: