Practice question

Mass number reflects total nucleons conserved unless alpha particle is ejected. In beta-minus decay, a neutron inside nucleus transforms into proton, electron, and antineutrino. Proton number rises by one, shifting element up one group, but total count of protons plus neutrons remains identical because neutron loss balances proton gain. Hence atomic mass unchanged. Alpha decay reduces mass by four, positron emission also preserves mass but decreases atomic number. Gamma decay emits only energy with no nucleon change. Therefore beta-minus decay exemplifies conservation of mass number during atomic number change.