What is the expression for the value of n of a particle of mass m in a one-dimensional box of length L such that the separation between neighboring levels is equal to the mean energy of thermal m?

A) E = n² \pi² \hbar²}}2mL²}}
B) E = n² \pi² \hbar²}}2mL}}
C) E = n \pi² \hbar²}}2mL²}}
D) E = n \pi² \hbar²}}2mL}}