Multiple choice general knowledge science & technology A star is a luminous ball of gas composed mainly of what Oxygen & Hydrogen Helium & Oxygen Krypton & Helium Hydrogen & Helium Reveal answer Fill a bubble to check yourself D Correct answer Explanation Stars are primarily composed of hydrogen (about 74% by mass) and helium (about 24%) through nuclear fusion. While oxygen exists in stars, it's not one of the two primary components.