Which of the following complexes is used as an anticancer agent?

$CO$ (Carbon monoxide) is a neutral oxide of carbon,but it acts as a very strong field ligand and associates with metals to form complex compounds. These complex compounds are very useful in metallurgical processes. $CO$ is a poisonous gas because:

Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is :

Select the incorrect match.

When conc. $H_2SO_4$ is treated with $K_4[Fe(CN)_6]$,$CO$ gas is evolved. If dilute $H_2SO_4$ is used instead of conc. $H_2SO_4$,the gas evolved is:

The metal cation present in sodium nitroprusside is also present in: