Doubly-Ionized Lithium Is a Hydrogen-Like Ion,in Which the Nucleus with Charge

Multiple Choice

Doubly-ionized lithium is a hydrogen-like ion,in which the nucleus with charge 3e is orbited by a single electron.What wavelength light would be emitted from Li⁺⁺ as the electron dropped from the n = 4 to the n = 3 orbit?

A) 16.9 µm
B) 1.88 µm
C) 470 nm
D) 208 nm