The difference between the wave number of 1st line of Balmer series and last line of Pasehen series for 20. ${\mathrm{Li}}^{2+}$ ion is:

$\left\{\left[\frac{1}{2^2}-\frac{1}{3^2}\right]-\left[\frac{1}{3^2}-\frac{1}{{\mathrm{\infty }}^2}\right]\right\}\times R_{\mathrm{H}}\times 9$

For ${\mathrm{Li}}^{2+}$ ions, there is a $\frac{\mathrm{R}}{4}$ difference in wave number between the first line of the Balmer series and the last line of the Paschen series.