Why did the era of nuclei end when the universe was about 380,000 ...

[tiara099]

Why did the era of nuclei end when the universe was about 380,000 years old?
 
  A) The nucleosynthesis era that produced the nuclei heavier than helium ended.
  B) Photons were finally able to escape the plasma of the early universe and were no longer available to produce hydrogen and helium nuclei.
  C) Atomic nuclei were finally able to escape the plasma of the early universe.
  D) The universe had expanded and cooled enough for stable, neutral atoms to form.
  E) All the free particles had combined to form the nuclei of atoms.

Question 2

Consider the star to which the arrow points. How is it currently generating energy?
 
  A) by core hydrogen fusion
  B) by hydrogen shell burning around an inert helium core
  C) by gravitational contraction
  D) by core helium fusion combined with hydrogen shell burning
  E) by both hydrogen and helium shell burning around an inert carbon core

[brbarasa]

Answer to Question 1

D

Answer to Question 2

B

[tiara099]

Excellent

[nathang24]

Gracias!