Question

which electrons of an atom are most reactive?
those that are the farthest away from the positive atomic nucleus
when they have a full shell
those that are nearest to the positive atomic nucleus
those that are nearest to a negative nucleus

Explanation:

Valence electrons, which are the electrons in the outermost shell (farthest from the positive atomic nucleus), are most involved in chemical reactions as they have the weakest attraction to the nucleus and can be easily shared, gained, or lost.

Answer:

those that are the farthest away from the positive atomic nucleus