a. 1s 2s 2p 3s 3p 4s 3d 4p is the correct option.
This gives the following order to fill the orbit: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s)
Aufbau's principle states that electrons fill low-energy atomic orbitals before they fill high-energy atomic orbitals. .. By following this rule, you can predict the electron configuration of an atom or ion.
There may be two electrons at the maximum of one orbit. Since the s subplane has only one orbit, it can hold up to two electrons. The p subplane has three orbitals, so it can hold up to six electrons. The d-subplane has five orbitals, so it can hold up to 10 electrons.
Learn more about electrons here:brainly.com/question/11316046
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