For the energy levels in an atom , which one of the following statement is correct ?

Options

A. Thre are seven principal electron energy levels
B. The second principal energy level can have 4 sub-energy levels and contain a maximum of 8 electrons
C. The M energy level can have a maximum of 32 electrons.
D. The 4s sub energy level is at a lower enerty than the 3d sub energy level.

Answer

A, D