Classify the reaction by their type. Note there may be more than one way to classify a reaction.

Cu (s) + 4 HNO₃ (aq) ⟶ Cu (NO₃) ₂ (aq) + 2 NO₂ (g) + 2 H₂O (l)

Redox reaction and single displacement

Explanation:

This reaction is first of all a redox reaction. A redox reaction is a reaction that involves both oxidation and reduction. Oxidation involves increase in oxidation number while reduction involves decrease in oxidation number.

Copper (Cu) had an oxidation number of "0" as a reactant but had an oxidation number of "2+" in the product [Cu (NO₃) ₂] hence oxidation occurred.

Nitrogen (N) had an oxidation number of "5+" in the reactant (HNO₃) but had an oxidation number of "4+" in the product (NO₂) hence reduction also occurred.

Also, from the reaction, it can be deduced that copper (Cu) displaced hydrogen (H) from the nitric acid (HNO₃) solution to form copper (II) nitrate [Cu (NO₃) ₂]. It should be noted that copper can displace hydrogen because it is higher than hydrogen in the electrochemical series. Hence, this reaction can also be called a single displacement reaction. A single displacement reaction is a reaction in which an atom of an element replaces another atom in a compound (as seen in the equation given in the question).