According to Hund's rule, when electrons occupy orbitals of equal energy, one electron enters each orbit until A. there are two electrons in each orbital. B. electron velocities become constant. C. all the orbitals contain one electron, with opposite spins. D. all the orbitals contain one electron, with spins parallel.

• hackman1216: Hund's Rule. Hund's rule: every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. so D. is the answer
• adefioyelaoye:

  According to Hund's rule, when electrons occupy orbitals of equal energy,

  one electron enters each orbit until all the orbittals contain one electron,

  with spins parallel.

  Hund's rule helps to reduce the repulsive forces which would have

  occurred in orbittals with the same spin.

  The  rule states that every orbital in a subshell is singly occupied with one

  electron before any of the orbitals are doubly occupied and all electrons in

  singly occupied orbitals have the same type of spin. This also explains why

  the spins are parallel.

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