Rydberg physics is the most exquisite playground for the exploration of quantum technologies. Therefore, in this spectral investigation based on weakest bound electron potential model theory (WBEPMT). The quantum defects and Rydberg energies of low-lying and high-lying spectral Rydberg energy sequence in the following configurations: 1s2ns2Se1/2 and 1s2np2Po1/2 in Lithium-like ions (Z=4-6) Beryllium (Be II), Boron (B III) and Carbon (C IV) are computed with their radial expected values. Total 43 low-lying energies and quantum defects are computed and compared with 25 low lying radial expected values. The results are in good agreement with the previously published experimental / theoretical results. Based on the good agreement of low-lying data, total 257 new values of high-lying Rydberg energies and quantum defects are computed with 575 radial expected values currently not listed at NIST. The deviation in both sets of data doesn’t exceed 1 cm-1 .