- T, F The first statement correctly lists three types of radioactive decay.
However, radioactive nuclei do not emit these particles because they
are stable. Instead, they emit them in an effort to bring an unstable
nucleus to a lower energy level, so the second statement is false.
- T, T, CE
Divide and conquer. The first statement is true: If an
element decays for one half-life, half of the original
sample remains. If it decays for two half-lives, one
quarter of the original sample remains. The second
statement is also true. Does the whole sentence make
sense? Yes. So fill in the CE oval.
- C In this problem, an atom of Rn (radon) with an atomic number of
86 and a mass number of 222 undergoes a change. What happens to it? All
of a sudden it’s a different element, Po (polonium), with an atomic number
of 84 and a mass number of 218. It lost 2 protons and 2 neutrons. The Rn
atom has undergone alpha decay. In fact, you can see that an alpha particle
—helium-4 nucleus—has been emitted as a part of the whole process.
We’re dealing with alpha decay, and (C) is correct.
- D To begin with, you can see that an electron has been emitted, so
that’s one way to know, right away, that we’re dealing with beta decay. You
can also see that the atom of I (iodine) has turned into something else—
xenon—because its atomic number increased from 53 to 54. But its mass
number stayed the same, so it looks as if a neutron was turned into a proton.
That’s beta decay, and (D) is correct.
