Select all that apply. 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 is: no change in mass and adding a proton to the nucleus .

Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.
There are two types of beta decay: beta minus and beta plus. 
In beta minus decay, neutron is converted to a proton and an electron and an electron antineutrino.
In beta plus decay, a proton is converted to a neutron and positron and an electron neutrino, so mass number does not change.