Final answer:
Among main-sequence stars, chemical composition does not change significantly along the spectral types OBAFGKM, while surface temperature, mass, and luminosity vary greatly. Luminosity exhibits a greater degree of change than mass when comparing the extreme spectral types O and M.
Step-by-step explanation:
The characteristic that does not vary much among ordinary, hydrogen-fusing (main-sequence) stars as you go along the spectral sequence OBAFGKM is chemical composition. Main-sequence stars exhibit significant variability in their surface temperature, mass, and luminosity. The spectral classes, in order from hottest to coolest, are O, B, A, F, G, K, M, L, T, and Y. The most massive stars (O type) are also the most luminous and hottest, while the M type stars are the least massive, luminous, and are the coolest. Differences in the spectra of stars are principally due to temperature rather than composition.
When comparing mass to luminosity regarding changes along the main sequence, luminosity changes by a larger factor from spectral types O to M, reflecting the wide range in energy output from the most to the least luminous stars.