<span>Valence is defined as number of electrons that are present in the outermost orbital. Oxygen is in the 16th column of the periodic table and the total number of valance electrons is determined by units place digit of the column position which is 6 for oxygen. The outermost orbital is the high energy level and there are two in that orbit. So the valance is +2.</span>
the answer is a it can be used as an energy source by organisms
Answer:
Summary of Excretion so yea :()
The first blank is hypertonic and the second blank is hypotonic