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.

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

Explanation:

If hydrogen absorption lines are very strong in the visible spectrum of a particular star that means the population of electron in n = 2 is very high so on being exited they absorb radiation in Balmer series and give rise to absorption spectrum. The average temperature required to excite electron in hydrogen atom from n=1 to n = 2   is 10000K .

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force