Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver?

a. In the metallurgy of silver and that of gold, the respective metal is leached with a dilute solution of NaCN or KCN in the presence of air (for O2).
b. CO is a better reducing agent at lower temperature range 500-800 K in the blast furnace to extract iron from oxide ore.