Concept: According to the basic concept of the electronic configuration of the element, the electron can be filled first in those shell which has least energy or (n +l) value. Here, n is the principal quantum number on shell and l is the azimuthal quantum number.
Since, the first shell has least value of energy in any atom. So, it should be filled first.
Hence, the correct statement can be written as;
When diagramming an atom, the electron shells _nearest to _ the nucleus must be filled first.
