N VII Lyα line emissivity (top), relative ion concentration (middle), and relative level occupation (bottom) of the two upper levels ²P_0.5 and ²P_1.5 (in sum, since the fine-structure lines cannot be distinguished). The underlying ionisation balance of Urdampilleta et al. (2017) and the proto-solar abundance of Lodders et al. (2009) is used. In a hot (kT ≳ 0.6 keV) single-temperature CIE plasma, nitrogen is almost fully ionised in the form of N VIII, i.e. the ion concentration of N VIII is ∼1. Most of the N VII is in the ground level ¹S_0.5, i.e. the level occupations of ¹S_0.5 is close to unity.