Answer:In chemistry, a valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
Explanation: hope this helped
D as the two substances could have close boiling points, so if the temperature is not controlled well, both substances will evaporate.
Sulfur is the answer according to the 2'8-8 rule