(c) Energy of helium ions. $E_{n}\ = \ -$ $\frac{13.6\ Z^{2}}{n^{2}}\ eV$ In minimum position, $n$=1 For $\ He^{+},\ Z = 2$ $E = \frac{- 13.6\ {\times \ (2)}^{2}}{1}\ eV$ $E = 54.4\ eV$
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