In $\mathrm { Li } ^ { + + }$, electron in first Bohr orbit is excited to a level by a radiation of wavelength $\lambda$. When the ion gets de-excited to the ground state in all possible ways (including intermediate emissions), a total of six spectral lines are observed. What is the value of $\lambda$?\\
(Given: $h = 6.63 \times 10 ^ { - 34 } \mathrm {~J}$ s ; $c = 3 \times 10 ^ { 8 } \mathrm {~m} \mathrm {~s} ^ { - 1 }$ )\\
(1) 10.8 nm\\
(2) 9.4 nm\\
(3) 11.4 nm\\
(4) 12.3 nm