When U-238 emits an alpha particle, the nucleus left behind has
A) 94 protons.
B) 90 protons.
C) 93 protons.
D) 91 protons.
E) 92 protons.

Question

Quizplus · Accepted Answer

When U-238 (uranium-238) emits an alpha particle, which consists of 2 protons and 2 neutrons, the atomic number decreases by 2. Since uranium has 92 protons, the resulting element has 90 protons, which corresponds to thorium (Th).

When U-238 Emits an Alpha Particle, the Nucleus Left Behind