According to the aufbau principle,
a. electrons enter orbitals of lowest energy first.
b. electrons enter orbitals of highest energy first.
c. an orbital may be occupied by only two electrons.
d. electrons in the same orbital must have opposite spins.

50.)the diagram below represents the wave fronts produced by a point source moving to the right in a uniformmedium. observers are located at points a and b.compared to the wave frequency and wavelength observed at point a, the wave observed at point b has a(1) higher frequency and a shorter wavelength(2) higher frequency and a longer wavelength(3) lower frequency and a shorter wavelength(4) lower frequency and a longer wavelength