What makes up 90 percent of interstellar gas? hints what makes up 90 percent of interstellar gas? hydrogen carbon dioxide helium carbon monoxide?

Despite being an extremely rare gas on Earth, hydrogen is the most common element in the universe. This is due to the fact that hydrogen is the fuel for stars, as it undergoes the fusion nuclear reaction to form helium and release the energy to sustain the star. Therefore, the answer to this question is hydrogen.