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# Mass Number

## Key Questions

Well, the mass number of an atom is simply the number of massive, nuclear particles, protons, and neutrons....

#### Explanation:

And so for ""^1H, the mass number is simply 1; for ""^2H, the mass number is simply 2; for ""^3H, the mass number is simply 3. The isotopes contain $\text{0, 1, 2 NEUTRONS}$ respectively.

Most of the heavier atoms have a range of isotopes, and the quoted atomic mass on the Table is the weighted average of the isotopic masses..