When an alpha particle is emitted from an unstable nucleus, the atomic mass number of the nucleus
A) increases by 2.
B) decreases by 4.
C) stays unchanged.
D) decreases by 2.
E) increases by 4.

Question

Quizplus · Accepted Answer

When an alpha particle (which consists of 2 protons and 2 neutrons) is emitted from a nucleus, the atomic mass number decreases by 4 because the nucleus loses 4 nucleons (2 protons and 2 neutrons).

When an Alpha Particle Is Emitted from an Unstable Nucleus