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.

Henry, whose mass is 95 kg, stands on a bathroom scale in an elevator. the scale reads 830 n for the first 2.4 s after the elevator starts moving, then 930 n for the next 2.4 s. part a what is the elevator's speed 4.8 s after starting? express your answer with the appropriate units.