Question

The mass of a `"_10^20Ne` atom is is 19.99244 amu. How do you calculate its mass defect?

Answer 1

By taking the difference between the sum of the nucleon masses and the atomic mass.

Explanation:

I will not consider electronic mass here. We know (the masses should have been provided in the question!) that the neutron mass is `1.008701*"amu"` and the proton mass is `1.007316*"amu"`.

Given `"10 protons"` and `"10 neutrons"`, there combined mass is `10xx{1.008701+1.007316}*"amu"=20.16017` `"amu"`.

And thus the mass defect is, `20.16017` `"amu"-19.99244` `"amu"`
`=0.16773*"amu"`. And this seems a rather large value? I would check this with your text, or with someone who deals with particle physics problems. You are in the chemistry section, and certainly I don't have a feel for the right order of magnitude here.