Final answer:
Sulfide (option D) is not the name of a cation; it is an anion with a 2- 2 charge. All other options listed (sodium, iron (III), magnesium, and ammonium) are cations with corresponding positive charges.
Step-by-step explanation:
The student asks which of the following is not the name of a cation:
- A. sodium
- B. iron (III)
- C. magnesium
- D. sulfide
- E. ammonium
The answer to this question is D. sulfide. A cation is a positively charged ion. Sodium, iron (III), and magnesium are all cations, with sodium typically forming a 1+ charge, iron (III) having a 3+ charge, and magnesium having a 2+ charge. Ammonium is also a cation with a 1+ charge.
Conversely, sulfide is an anion with a 2- charge and thus not a cation. Each of the other options, namely sodium, iron (III), magnesium, and ammonium, exists in ionic forms with positive charges.