Question

The emission of a Beta particle has the effect of:



decreasing mass by one unit

increasing mass by one unit

no change in mass

adding a proton to the nucleus

Answer 1

In beta emission, a neutron decays to form a proton, an electron and an antineutrino. The atomic number increases by 1 and the mass number stays the same. The mass of the nucleus decreases by the mass of an electron and the antineutrino, which is almost mass-less.

By the way, the choices are a little off-base because the atom is not increasing or decreasing mass by one unit, it's changing the MASS NUMBER by 1. There is a difference between the mass of an isotope and the mass number of an isotope. The mass number is always an integer -- it's a "counting number" -- because you're counting the nucleons -- the particles in the nucleus. The actual mass of an isotope cannot be inferred from the mass number (although it is close), and the actual mass is usually known to 3, 4 or even 5 decimal places.