The energy levels available to each electron in a system of N non-interacting electrons are En = nE0, n = 0,1,2, ... A magnetic field, which does not affect the energy spectrum, but completely polarizes the electron spins, is applied to the system. The change in the ground state energy of the system is
1
\(\frac{1}{2} N^2 E_0\)
2
N2E0
3
\(\frac{1}{8} N^2 E_0\)
4
\(\frac{1}{4} N^2 E_0\)