Which particle is approximately 1838 times heavier than an electron?

• A. Proton
• B. Neutron
• C. Electron
• D. Photon

Answer: (A)

Mass comparisons show that nucleons are vastly heavier than the electron. The proton has a rest mass of about 1.007 atomic mass units, while the electron is about 0.0005486 u. Dividing gives a ratio near 1836, which is in the same ballpark as 1838. This is why the proton is the best match for “approximately 1838 times heavier.” The neutron is even closer to 1839, but in this context the proton is the standard example used for that approximate factor. The electron isn’t heavier, and the photon has zero rest mass, so neither of those fit.