Video Transcript
Which subatomic particle A is emitted when the following unstable isotope of fluorine decomposes? (A) Neutron, (B) quark, (C) electron, (D) positron, or (E) proton.
The given equation represents the unstable isotope fluorine-18 undergoing radioactive decay to form a different element, in this case oxygen-17, while also emitting a subatomic particle represented here by A. Radioactive decay is the process by which an unstable nucleus spontaneously emits particles or radiation. The question indicates that in this radioactive decay process, a subatomic particle was emitted. We can uncover the identity of subatomic particle A by considering that reactants and products in a nuclear equation must be equivalent in total mass number represented here by A, which can be calculated for nuclei by finding the sum of the protons and neutrons.
For example, our reactant fluorine-18 has a mass number of 18, and therefore 18 must be the sum of its protons and neutrons, while our product oxygen-17 has a mass number of 17. And we need to determine the mass number of particle A. Reactants and products in nuclear equations must also be equivalent in total charge represented here by Z, which is the charge of the particle to which it refers, and for nuclei is equal to the number of protons. Our reactant fluorine-18 is not a subatomic particle. So, we know the number nine indicates the number of protons in its nucleus, while oxygen-17 has eight protons. We can use this information to determine the charge of particle A.
Let’s compare mass numbers of the reactants and products. The only reactant given in the equation is fluorine-18. So, the total mass number of the reactants is 18, and the mass number we are given in the products is 17 from oxygen-17. So, for the total mass number of the reactants to be equal to the total mass number of the products, we must add one to the products. And therefore, subatomic particle A must have a mass number of one.
Let’s repeat this process to determine the charge of particle A. Fluorine-18 has nine protons, while oxygen-17 has eight protons. So to make this expression true, we must add one to the products. And therefore, subatomic particle A must have a charge of positive one.
Let’s look at the answer choices. Answer choice (A), a neutron, has a mass number of one but is a neutral particle and therefore has a charge of zero. We can eliminate answer choice (A). Answer choice (B), a quark, is a fundamental particle which makes up neutrons and protons. So its mass would be much smaller than a proton or neutron as would its charge. We can eliminate answer choice (B). Answer choice (C), an electron, has a mass so much smaller than a proton or neutron that it is given a mass number of zero and a charge of negative one. So, we can eliminate answer choice (C). Answer choice (D), a positron, is a subatomic particle with a mass number identical to that of an electron with an opposite charge of positive one. We can eliminate answer choice (D) as well.
Finally, answer choice (E), a proton, has a mass number of one and a positive one charge. This matches both the mass number and charge we found for subatomic particle A. Therefore, the correct answer is (E) proton.
