Final answer:
Typical features of quasar absorption lines in intergalactic clouds include broad hydrogen lines and weak heavy element lines at higher redshifts. Radio telescopes play a key role in detecting hydrogen in interstellar space.
Step-by-step explanation:
The typical features seen in quasar absorption lines of intergalactic clouds are generally as follows: The hydrogen lines are broader and lines from heavy elements are weaker at higher redshifts. This can be understood from the nature of hydrogen at interstellar temperatures where it does not absorb light in the visible part of the spectrum. However, heavy elements like calcium and sodium can produce absorption lines at these temperatures, detectable in sensitive observations.
With increasing redshift, resulting from the expansion of the universe, the spectral lines of these elements shift to longer wavelengths. While neutral hydrogen lacks spectral features in the visible spectrum, excited hydrogen (such as in the Balmer series) does show absorption lines, but these are absent in the cold interstellar medium where hydrogen is in the ground state. Radio telescopes have therefore been instrumental in studying interstellar hydrogen through the detection of radio emissions and absorption.