Atomic structure and the Periodic Table — practice question

Refer to the Periodic Table to answer this question. Which two particles contain the same number of electrons?

• A$\text{Ar}$ and $\text{Ca}$
• B$\text{Na}^{+}$ and $\text{K}^{+}$
• C$\text{Fe}^{2+}$ and $\text{Fe}^{3+}$
• D$\text{Ca}^{2+}$ and $\text{Sc}^{3+}$