The $\pi-$acid ligand which uses its $d-$orbital during synergic bonding in its complex compound.

Which of the following is the most stable complex?

$CuSO_4$ solution reacts with excess of $KCN$ solution to form:

When aqueous sodium hydroxide is added to an aqueous solution of chromium $(III)$ ions,a green-blue precipitate is first formed which re-dissolves to give a green solution. This green colour is due to

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:

Which one of the following complexes is violet in colour?