Answer
122 eV
Work Step by Step
Doubly ionized lithium is similar to hydrogen. The difference is that there are 3 protons in the nucleus.
Ionizing the $Li^{2+}$ means removing the electron. This is the same as raising the electron to zero energy.
Use equation 27–15b with Z=3 and n = 1.
$$E_{ionization}=0-E_1$$
$$=0-\frac{-13.6eV(Z^2)}{1^2}=122eV$$
