(b) E$_{1}$ = $- 13.6\ –( - 3.4)\ = \ - 10.$2 eV
$E_{2}\ $= $- \ 3.4\ –\ (\ - \ 13.6)\ = \ + \ 10.$2 eV
$E_{3}$ =$\ - \ 0.136\ –\ (\ - 1.51)\ = \ - \ 1.374$ eV
$E_{4}\ =$ $- \ 1.51\ –\ (\ - \ 0.136)\ = - \ 1.374\ $eV
When an electron makes transition from higher energy level having energy $E_{2}(n_{2})\ $to lower energy level having energy$E_{1}(n_{1})$, then a photon of frequency $v$ is emitted.
Here, for emission line $E_{1}\ $is maximum hence, it will have the highest frequency emission line.