The combination of copper II nitrate and sodium hydroxide results in the formation of copper II hydroxide and sodium nitrate. It is a double exchange reaction, which means that the two reactant compounds (copper II nitrate and sodium hydroxide) switched ions to form two new product compounds.
The combination of copper II nitrate and sodium hydroxide can also be referred to as a double displacement reaction. Reactions that are called double displacement reactions often include precipitation reactions, gas forming reactions and neutralization reactions. For example, sodium hydroxide is a strong base, and when it's added to copper II nitrate, the result is the precipitation of insoluble copper hydroxide or a double displacement reaction.