What is the mass of a neutron?

The mass of a neutron is approximately 1 atomic mass unit (amu), which is defined as 1/12th of the mass of a carbon-12 atom. In terms of grams, this value is about 1.67 x 10^-27 kg. Neutrons are one of the primary subatomic particles found in the nucleus of atoms, along with protons, and their mass is significantly greater than that of electrons, which have a negligible mass relative to protons and neutrons.

The choice indicating that the mass is "almost 0" misrepresents the actual mass of neutrons since they contribute substantially to the atomic mass of an element. The options suggesting the mass of 2 or 0.5 would suggest a misunderstanding of neutron mass, as they are not accurate reflections of what we know from data on atomic structure. Thus, 1 is the proper and commonly accepted measurement representing the mass of a neutron.