An atom that has only one electron in its valence electron shell is chemically reactive. a. not b. mildly c. highly d. the name of the element is needed to figure this out.

The option C is correct option. And full statement is "An atom that has only one electron in its valence electron shell is highly chemically reactive".

Explanation:

Valence electron means electron in outer shell.Reactivity of an atom depends upon the ability to give or take electron from other atoms.As above described, this atom has only one electron and to get stability, it will readily give electron to other atom.Stability of atom is a state when an atom has filled outer shell.Hence to get stable atom will highly reactive towards other atoms.

It’s a) absolute dating