2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/219344Theoretical consistency of the 3-3-1 model with right-handed neutrinos demands that the number of family of fermions be exactly equal to three. In this brief report we show that such theoretical requirement results in a clean and severe bound on the Z-Z$^{\prime}$ mixing angle: $-3,979\times 10^{-3}<ϕ<1,309\times 10^{-4} {with 90% CL}$.Minor modification in the conclusions, some refs added, to appear at MPLAHigh Energy Physics - Phenomenologytext