When Cu reacts with AgNO₃ solution, the reaction takes . The formula of corrosive sublimate is place is

Cu is placed above Ag in electrochemical series, hence it can replace Ag from its salts solution. Therefore the reaction occur as follows 

$\stackrel{ }{\stackrel{0}{\mathrm{Cu}}+\stackrel{+1}{\mathrm{Ag}}{\mathrm{NO}}_3}\stackrel{ }{\mathrm{ }\stackrel{\mathrm{oxidation}}{\to }\mathrm{ }}\stackrel{+1}{\mathrm{C}}{\mathrm{uNO}}_3+\mathrm{Ag}$