Which color of light is absorbed by an aqueous solution of $CuSO_4$?

Sodium thiosulphate is used in photography for which of the following purposes?

Identify the complexes formed in the following processes:
$I$. Mond's process for purification of nickel
$II$. Removal of unreacted $AgBr$ from photographic plates
$III$. Removal of lead poisoning from the body

$CO$ (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:

In any ferric salt,on adding potassium ferrocyanide,a Prussian blue colour is obtained,which is:

The substance used in the treatment of cancer is ........