When an unstable nucleus decays by emitting an alpha particle, the atomic number of the nucleus
A) increases by 4.
B) increases by 2.
C) decreases by 2.
D) decreases by 4.
E) remains unchanged.

Question

Quizplus · Accepted Answer

An alpha particle is a helium nucleus, which consists of two protons and two neutrons. Therefore, the atomic number of the parent nucleus decreases by 2, since it loses two protons. The mass number also decreases by 4, since the alpha particle has a mass number of 4.

When an Unstable Nucleus Decays by Emitting an Alpha Particle