A sample of heavy, oxygen-18 enriched water, 2H218O^{2}\text{H}_2^{18}\text{O}2H218O, has a total mass of 2.20 g.
What is the total number of neutrons in this sample?
(The Avogadro constant, L=6.02×1023 mol−1L = 6.02 \times 10^{23}\text{ mol}^{-1}L=6.02×1023 mol−1. Assume the atomic number of hydrogen is 1 and the atomic number of oxygen is 8. Assume the isotopic masses of 2H^{2}\text{H}2H and 18O^{18}\text{O}18O are 2.0 g mol-1 and 18.0 g mol-1 respectively.)
6.02×10236.02 \times 10^{23}6.02×1023
7.22×10237.22 \times 10^{23}7.22×1023
7.95×10237.95 \times 10^{23}7.95×1023
8.43×10238.43 \times 10^{23}8.43×1023