Stacked spectrum of QSO2 candidates with normalised median flux in the rest-frame wavelength, obtained through spline interpolation using available SDSS spectra. The spectrum is additionally normalised based on the number of contributing spectra for each rest-frame wavelength. Grey vertical lines mark the positions of emission lines in the rest frame. The plot includes two zoomed-in regions: (1) 3326–3526 Å, highlighting the [NeV]λ3426 emission line, and (2) 3630–3830 Å, highlighting the [OII]λλ3727, 3730 emission lines. The red line represents the Gaussian fit applied to the spectrum.