The Pontecorvo, Maki, Nakagawa and Sakata (PMNS) neutrino-mixing matrix is in the Scale-Symmetric Theory (SST) the unitary mixing matrix which contains information on states of neutrinos when they collide with the neutrinos in the Cosmic Neutrino Background (CNB). Since in SST there are only 3 Dirac neutrino flavours (there are not in existence Majorana neutrinos) and because the CP phase is equal to 180 degrees, the PMNS matrix is parameterized by three mixing angles only that are calculated from three fundamental weak phenomena that took place in the nuclear plasma at the beginning of the expansion of the Universe - it fixed the abundances of different flavours in CNB. Calculated mixing angles A(ij) are A(13) = 8.2654, A(12) = 33.0616 and A(23) = 41.3250 degrees. We showed that the mixing angle A(13) follows from internal structure of pions and from the atom-like structure of baryons. The ratios of the mixing angles are as 1 : 4 : 5 and they represent respectively one stable flavour (i.e. electron- or muon-neutrino), two entangled flavours (i.e. electron- or muon- plus tau-neutrino i.e. four entangled stable neutrinos), and three entangled flavours (i.e. electron- plus muon- plus tau-neutrino i.e. five entangled stable neutrinos). We as well calculated the degenerate masses of the three different neutrinos - calculated sum is 0.287 eV (it is consistent with experimental data). We calculated mass of tauon (1777.2 MeV), which is an analog to muon. We answered following question: Why neutrinos are left-handed whereas antineutrinos are right-handed? SST shows that sterile neutrinos are not in existence. The matter-antimatter asymmetry follows from the left-handedness of the Higgs-field components.