A nucleus with mass number A and atomic number Z emits an alpha particle. The mass number and atomic number, respectively, of the daughter nucleus are:
A) A, Z -2
B) A - 2, Z - 2
C) A - 2, Z
D) A - 4, Z
E) A - 4, Z - 2

Question

Quizplus · Accepted Answer

When a nucleus emits an alpha particle, it loses 2 protons and 2 neutrons. An alpha particle has a mass number of 4 (2 protons + 2 neutrons) and an atomic number of 2 (2 protons). Therefore, the daughter nucleus will have a mass number decreased by 4 (A - 4) and an atomic number decreased by 2 (Z - 2).

A Nucleus with Mass Number a and Atomic Number Z