An Alkali Metal Atom Is in the Ground State

An alkali metal atom is in the ground state.The orbital angular momentum equals zero and the spin angular momentum is entirely due to the single valence electron.A magnetic field is applied that splits the ground state energy level into two levels,27 μeV apart.What is the strength of the applied magnetic field? (h = 6.626 × 10^-34 J ∙ s,Bohr magneton = μ_B = ,1 eV = 1.60 × 10^-19 J)

A) 0.23 T
B) 0.18 T
C) 0.29 T
D) 0.34 T
E) 0.40 T