1. The problem statement, all variables and given/known data The deuteron is a bound state between a proton and a neutron (and the nucleus of the H2 isotope). The binding energy of the deuteron is 2.2MeV. What is the mass of the deuteron? 2. Relevant equations Mp = 938.3 MeV/c^2 Mn = 939.6 MeV/c^2 3. The attempt at a solution Md = 938.3 + 939.6 - 2.2/c^2 = 1877.9 MeV I tried to look for that number online, but I've only found numbers closer to 1875.7 MeV/c^2, which suggests to me that the binding energy changes the mass more than I found it to. Where am I going wrong? Should I not be dividing the binding energy by c^2? Thanks for any help!