In an atom, the electrons at the outermost energy level is called as valence electrons. It is the valence electrons which participates and interacts with the other atoms and form bonds. The valence electrons of an atoms are important as they depict the chemical properties of an element.
Thus the valence electrons resides the outermost shell and surrounds the atomic nucleus.
A constant is something that is kept the same throughout the course of a experiment. So I would guess C) because they are not doing anything special. If it’s not C then it is A. :)
