The ionization energy of hydrogen atom is $1314 \mathrm{kJ} {\mathrm{mol}}^{-1}$.The ionization energy of ${\mathrm{He}}^{+}$ ion is expected to be 

Since $E\propto -Z^2/n^2$,we have

 $$\begin{gathered} \frac{E_1\left({\mathrm{He}}^{+}\right)}{E_1\left(\mathrm{H}\right)}=\frac{-4/1}{-1/1}=4 \\ \Rightarrow E_1\left({\mathrm{He}}^{+}\right)=4E_1\left(\mathrm{H}\right) \end{gathered}$$

Hence,

   $$\begin{gathered} \mathrm{IE}\left({\mathrm{He}}^{+}\right)=4\mathrm{IE}\left(\mathrm{H}\right) \\ =4\times 1314 \mathrm{kJ}{ \mathrm{mol}}^{-1} \\ =5256 \mathrm{kJ}{ \mathrm{mol}}^{-1} \end{gathered}$$