Kaplan Nursing Entrance Practice Exam

What do carbon-12 and carbon-14 have in common?

1. Number of protons

2. Number of neutrons

3. Molecular weight

4. Type of chemical bond

The correct answer is: Number of protons

Carbon-12 and carbon-14 are both isotopes of the element carbon, which means they share the same number of protons, specifically six. The chemical identity of an element is defined by the number of protons in its nucleus; therefore, all isotopes of carbon will have that consistent count of six protons. While carbon-12 and carbon-14 differ in their number of neutrons—carbon-12 has six neutrons and carbon-14 has eight—they still maintain the same number of protons, reinforcing their identity as carbon isotopes. Other options relate to different properties that vary between the isotopes. Molecular weight would differ due to the variation in the number of neutrons, and type of chemical bond does not pertain specifically to the isotopes themselves but rather to how carbon can bond chemically, which is not fundamental to the isotopic distinction.