Radio Astronomers Often Study the Radiation Emitted by a Hydrogen $21 \mathrm {~cm}$

Short Answer

Radio astronomers often study the radiation emitted by a hydrogen atom from a transition between the two hyperfine levels associated with the ground state. This radiation has a wavelength of $21 \mathrm {~cm}$ . What is the energy difference between the hyperfine levels? $( 1 \mathrm { eV } = 1.60 \times$ 10^-19J)
A) $5.9 \times 10 ^ { - 6 } \mathrm { eV }$
B) $4.7 \times 10 ^ { - 25 } \mathrm {~J}$
C) $5.9 \times 10 ^ { - 25 } \mathrm {~J}$
D) $1.7 \times 10 ^ { - 24 } \mathrm {~J}$