Chemistry · Structure of atom

An atomic species has 18 electrons, 19 protons, and 20 neutrons. What is its correct symbol?

1. A
   \( {}_{19}^{39}\text{K}^- \)
2. B
   \( {}_{19}^{39}\text{K}^+ \)
3. C
   \( {}_{20}^{39}\text{Ca}^{2+} \)
4. D
   \( {}_{18}^{38}\text{Ar} \)