What is the primary composition of stars?

• A. 70% hydrogen and 30% helium
• B. 90% hydrogen and 10% helium
• C. 80% hydrogen and 20% helium
• D. 100% hydrogen

Answer: (B)

Stars are composed mostly of hydrogen, with helium as the second-most abundant element; metals and other elements are only a small fraction. In the Sun, hydrogen makes up roughly three-quarters of the mass, while helium is about a quarter. The key idea being tested is that hydrogen dominates the makeup of stars. Among the options, the one that shows hydrogen in a large majority communicates this dominance most clearly, reflecting the general reality that hydrogen is the primary component in stars. Keep in mind that actual stellar compositions vary and the exact ratios aren’t fixed, but the overarching point is that hydrogen is the main constituent.