Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2025 / 2 / a / ii / Solution

The lowest two energy levels have $n=1$ and $n=2$. For carbon, $Z=6$, even though the ion's net charge is $5+$:Increasing $n$ raises the energy toward zero; the most negative value is the ground-state energy.