When A $\beta ^ { - }$ Particle Is Emitted from an Unstable Nucleus, the Atomic Mass

Multiple Choice

When a $\beta ^ { - }$ particle is emitted from an unstable nucleus, the atomic mass number of the nucleus

A) increases by 1 .
B) decreases by 2 .
C) decreases by 1 .
D) increases by 2 .
E) does not change.