Chemistry - Ionic Equilibrium Question with Solution | TestHub

According to Lewis acid-base concept, bases are electron pair donor and acids are electron pair acceptor. In reaction
$4\mathrm{N}{\mathrm{H}}_3+\left[\mathrm{C}\mathrm{u}\right({\mathrm{H}}_2\mathrm{O}{)}_4{]}^{2+}\rightleftharpoons \left[\mathrm{C}\mathrm{u}\right(\mathrm{N}{\mathrm{H}}_3{)}_4{]}^{2+}+4{\mathrm{H}}_2\mathrm{O}$
$\mathrm{N}{\mathrm{H}}_3$molecules donates electron pairs, so it is a Lewis base and$\mathrm{C}{\mathrm{u}}^{2+}$accepts the electron pairs donated by the$\mathrm{N}{\mathrm{H}}_3$molecules, so it acts as Lewis acid.