Final answer:
A sodium atom would be larger than a sodium cation because cations are always smaller than their respective neutral atoms. Thus, the correct answer is B. a sodium atom.
Step-by-step explanation:
The question asks which of the following would be larger than a sodium cation. According to the information provided, cations are always smaller than the neutral atom and anions are always larger than the neutral atom they derive from. In comparing the sizes, a sodium atom, which has an equal number of protons and electrons (11), will be larger than a sodium cation (Na+) because the cation has lost an electron and thus has a closed shell, making it smaller. Therefore, the correct answer is: B. a sodium atom.
Looking at the other options:
- A helium atom is smaller than a sodium cation because it only has two protons and two electrons.
- A lithium ion, which is likely to be Li+, would be smaller than a sodium cation as lithium is above sodium in the periodic table and ions generally get larger as you move down a group.
- A hydrogen ion (H+) is essentially a proton without an electron and is thus smaller than a sodium cation.