Which of the following figures represents the beta decay of Mg to give Al after one half-life has passed? Unshaded spheres represent Mg atoms and shaded spheres represent Al atoms.

Question

Which of the following figures represents the beta decay of  Mg to give  Al after one half-life has passed? Unshaded spheres represent  Mg atoms and shaded spheres represent  Al atoms.

Quizplus · Accepted Answer

In beta decay, a neutron within a nucleus is converted into a proton and an electron (beta particle), which is emitted from the nucleus. The amount of protons in the nucleus increases by one, which changes the identity of the atom. 
Looking at the figures, we can see that figure 2 shows the correct transformation of a Mg atom into an Al atom after one half-life has passed. The unshaded sphere represents the original Mg atom, and the shaded sphere represents the newly formed Al atom. In figure 1, the atomic number remains the same, which is not possible in beta decay. Figure 3 shows a decrease in atomic number, which is not possible in beta decay either. Figure 4 shows an increase in atomic number, but with the wrong number of protons and neutrons, so it is also not a possible representation of beta decay.

Which of the Following Figures Represents the Beta Decay of