(d)
$E_{1} - E_{2} = 1312 \times Z^{2}\left\lbrack \frac{1}{1^{2}} - \frac{1}{2^{2}} \right\rbrack$
$E_{1} - E_{2} = 1312 \times Z^{2}\left\lbrack \frac{3}{4} \right\rbrack\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ldots(i)$
$E_{2} - E_{3} = 1312 \times Z^{2}\left\lbrack \frac{1}{2^{2}} - \frac{1}{3^{2}} \right\rbrack$
$E_{2} - E_{3} = 1312 \times Z^{2}\left\lbrack \frac{5}{36} \right\rbrack\ \ \ \ \ \ \ \ \ \ \ \ \ldots(ii)$
From Eqs. (i) and (ii)
$\frac{E_{1} - E_{2}}{E_{2} - E_{3}} = \frac{3 \times 36}{4 \times 5} = \frac{27}{5}$