In the visible spectra of stars, absorption lines of hydrogen are produced when atoms are excited from n = 2 to higher levels (the Balmer series). If hydrogen absorption lines are very strong in the visible spectrum of a particular star, what is this star's surface temperature?
1. relatively low temperature, about 6000 K (similar to the Sun), because at lower temperatures too many hydrogen atoms are in the ground (n = 1) state, and at higher temperatures too many have had their electrons completely ejected.
2. very high temperature, about 40,000 K, because at lower temperatures too many hydrogen atoms have their electrons in the ground state (n = 1) and cannot absorb in the Balmer series.
3. relatively high temperature, about 10,000 K, so that significant numbers of electrons are excited from the ground state, n = 1, to the first excited state, n = 2, but not too many of them have been ejected completely from the atoms.
4. very low temperature, 3000 K, because at higher temperatures so many hydrogen atoms have had their electrons completely ejected and cannot absorb in the Balmer series.