Cation electron configuration

Question

Which of the following actions will have the electron configuration 1s²2s²2p⁶3s²3p⁶

- Ca²⁺

- Co²⁺

- Scl⁺

- Cll⁺

Answer 1

This is the electron configuration of argon (Ar), and the only one in the list that is iso-electronic with Ar is Ca²⁺.  I have no idea what SCl⁺ and Cll⁺ are supposed to represent.