Question

The property of nitric acid that helps it to react with copper is

Answer 1

Nitric acid is an oxidizing agent and the reaction is not the usual acid + metal reaction. The products are oxides of nitrogen instead of hydrogen. The actual nitrogen oxide formed depends on the concentration and temperature of the acid.

There are actually two equations for the reaction of copper with nitric acid. It depends on whether the nitric acid is concentrated or not. If it is concentrated and in excess then the ratio is 1:4 copper to nitric acid. If it is dilute then the ratio is 3:8.

Answer 2

Cu+4HNOX3⟶Cu(NOX3)X2+2HX2O+2NOX2

It is not the "acid" part of nitric acid that reacts, but rather the nitrate anions. As you can see from the equation, nitrogen is reduced from the +5 oxidation state in NO3- to the +4 oxidation state in NO2.