Five Electrons Are in a Two-Dimensional Square Potential Energy Well

Multiple Choice

Five electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where n_x and n_y are integers. In units of (h²/8mL²) the energy of the first excited state of the system is:

A) 13
B) 22
C) 24
D) 25
E) 27