The wavelength of the first line of the $\mathrm{He}^{+}$ ion spectral series whose interval between the extreme lines is $2.725 \times 10^{6} \mathrm{~m}^{-1}$ is $\left(R=1.09 \times 10^{7} \mathrm{~m}^{-1}\right)$
(a) $471.82 \mathrm{~nm}$
(b) $4718.2 \mathrm{~nm}$
(c) $1019.37 \mathrm{~nm}$
(d) $165.14 \mathrm{~nm}$