Therefore, although the H atoms outnumber the metals by about 105 to 1, the metals provide the strongest lines in the solar spectrum. Note 105 100,000. The answer can be developed from the Bohr model H atoms just discussed. Detection of the former series requires access to a telescope above the Earth's atmosphere. Also, the fact that the infrared is not so easily observed as the visible part of the spectrum also ensures the prominence of the Balmer series.
Ionization can also occur through a collision with a particle.
As the temperature increases, the average speed and energy of the particles increases. Then the rate of ionization through collisions increases. The increasing ionization rate for temperatures in excess of about 10,000 K means the number of H atoms decreases. The decreasing atom density leads to a weakening of the hydrogen absorption lines. The answer is contained with Q1 above.