Answer: Technically, this cannot be answered, since none of the H atoms have a mass number assigned. With the assumption noted delow, I calculate 1.012 as the average atomic mass.
Explanation:
My answer is based on assumed masses for the three H isotopes:
1H : 1 AMU
2H: 2 AMU Deuterium
3H: 3AMU Tritium
AMU Rel Abund. Wt. Avg
1H 1 99.00% 0.99
2H 2 0.80% 0.016
3H 3 0.20% 0.006
Sum 1.012
