When a few drops of sodium hydroxide solution is added to copper nitrate solution, light blue colour ppt. of copper hydroxide is formed. This ppt. is insoluble in excess $\mathrm{NaOH}$ .
$\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathit{a}\mathit{q}\right)+2\mathrm{NaOH}\to$ $\underset{\mathrm{Light}\mathrm{Blue}}{\mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathit{s}\right)}+2{\mathrm{NaNO}}_3\left(\mathit{a}\mathit{q}\right)$