When a star exhausts its hydrogen fuel, what elements are produced?

When a star exhausts its hydrogen fuel, what elements are produced?

• A. It makes larger elements up to iron
• B. It creates only hydrogen again
• C. It creates only helium
• D. It dissolves into gas

Answer: (A)

When hydrogen fusion ends, the star’s core contracts and heats up enough to start fusing helium. This next stage builds up heavier elements: helium nuclei fuse to form carbon, and carbon can capture more helium to become oxygen. In stars with enough mass, the fusion chain continues through even heavier elements—neon, magnesium, silicon, and others—piling up elements all the way to iron in the core. Iron is the practical stopping point for steady fusion in a star because fusing iron doesn’t release energy. Heavier elements aren’t produced by normal fusion in the star’s life; they’re mainly formed later in the explosive supernova. So the produced elements span from helium up to iron during the star’s evolution, which is why the statement that larger elements up to iron are produced is the best fit.

When hydrogen fusion ends, the star’s core contracts and heats up enough to start fusing helium. This next stage builds up heavier elements: helium nuclei fuse to form carbon, and carbon can capture more helium to become oxygen. In stars with enough mass, the fusion chain continues through even heavier elements—neon, magnesium, silicon, and others—piling up elements all the way to iron in the core. Iron is the practical stopping point for steady fusion in a star because fusing iron doesn’t release energy. Heavier elements aren’t produced by normal fusion in the star’s life; they’re mainly formed later in the explosive supernova. So the produced elements span from helium up to iron during the star’s evolution, which is why the statement that larger elements up to iron are produced is the best fit.