The energy of separation of an electron is $30.6eV$ moving in an orbit of $L{i}^{2+}$. The number of waves made by the electron in one complete revolution in the orbit is:

As the energy of separation of an electron is $30.6eV$ means it has this much energy in the ground state.

By calculation, as $E=-\frac{13.6Z^2}{n^2}$;

Here $Z$ is $3$, $n=2$

So, the number of waves made by the electron in one complete revolution in the orbit is $2$.