Final answer:
Main sequence stars have neutral and ionized metal lines in their spectra, with spectral types A and G being representative examples. As stars evolve, they leave the main sequence, changing their position on the H-R diagram.
Step-by-step explanation:
The type of star that has both neutral and ionized metal lines is a main sequence star. The presence of these spectral lines indicates the star's temperature and the ionization level of the metals within its atmosphere. For example, spectral types A and G main-sequence stars, like our Sun, have such lines in their spectra.
Main-sequence stars derive their energy from the fusion of hydrogen into helium. As main-sequence stars age, they consume their nuclear fuel and eventually evolve into giants or supergiants, and they may ultimately end up as white dwarfs. These latter stages of a star's life see changes in luminosity and surface temperature, causing them to move off the main sequence on the Hertzsprung-Russell diagram, also known as the H-R diagram.
In summary, the main sequence stage includes stars of various spectral types (like A and G), which will display the characteristic neutral and ionized metal lines. The main sequence on the H-R diagram represents about 90% of the stars, while the other regions account for the later evolutionary stages such as giants, supergiants, and white dwarfs.