A Highly Ionized Atom With $Z = 5$ Has Only One Electron Left Around It, in Its Ground

Multiple Choice

A highly ionized atom with $Z = 5$ has only one electron left around it, in its ground state. How much more energy is required to finish the job and have a bare nucleus?

A) $13.1 \mathrm { eV }$
B) $10.9 \mathrm { eV }$
C) $68.0 \mathrm { eV }$
D) $340.0 \mathrm { eV }$