The emission of a beta particle has the effect a. decreasing mass by one unit /b. increasing mass by one unit / c. - no change in mass /d.- adding a proton to the nucleus / e. adding a proton of zero mass to the nucleus

The emission of a beta particle has the effect of : C. No change in mass

basically, beta particle has a very very little mass compared to the proton and  neutrons, so  little to the point that it never considered as a change in mass. But it does decreases the charge of atom

hope this helps