Which of the following is NOT a cation?

• A. Cl^-
• B. K^+
• C. Ca^{2+}
• D. Na^+

Answer: (A)

Verified step by step guidance

1. Recall that a cation is a positively charged ion, meaning it has lost one or more electrons.
2. Identify the charge on each ion given: \(\mathrm{K}^+\) has a positive charge, \(\mathrm{Ca}^{2+}\) has a double positive charge, and \(\mathrm{Na}^+\) has a positive charge.
3. Recognize that \(\mathrm{Cl}^-\) has a negative charge, indicating it has gained an electron and is therefore an anion, not a cation.
4. Compare the charges of all ions to determine which one is NOT a cation by looking for the ion with a negative charge.
5. Conclude that \(\mathrm{Cl}^-\) is NOT a cation because it carries a negative charge, unlike the other positively charged ions.