Electrons enter into orbitals in order of increasing energy as exemplified by?

A. 1S²2S²2PX²2py²2pz⁰3s⁰
B. 1S²2S²2PX²2py¹2pz¹3s⁰
C. 1S²2S²2PX¹2py¹2pz¹3s¹
D. 1S²2S²2PX²2py²2pz⁰3s¹

Correct Answer:

Option C – 1S²2S²2PX¹2py¹2pz¹3s¹

Explanation

Shells and subshells are filled in energy level order, so electrons will fill the 4s subshell before the 3d shell.

And the x subshell before the y and z.