Question

1. Select all that apply. Which of the following statements is true?

A. Primordial nucleosynthesis did not take place during the first three minutes of the universe because the temperature of the universe was sufficiently high to immediately dissociate any deuterium formed.
B. Once the temperature of the universe dropped below 9 × 10⁸ K, protons and neutrons fused, forming deuterium, and deuterium then fused with other particles, forming primarily helium.

C. Primordial nucleosynthesis ended when the density and temperature of the universe dropped too low for fusion to continue.
D. Primordial nucleosynthesis ended about 400,000 years after the Big Bang.

2. Fusion in stars does not significantly change the abundance of deuterium in the universe. Measurements of the primordial abundance of deuterium imply that:

A. The mass density of normal matter (protons and neutrons) is 4% of the critical value.
B. The mass density of normal matter is 23% of the critical value.     

C. The mass density of normal matter is 27% of the critical value.
D. The mass density of normal matter is 73% of the critical value.
E. The mass density of normal matter is 100% of the critical value.
F. The mass density of all matter is 4% of the critical value.
G. The mass density of all matter is 23% of the critical value.
H. The mass density of all matter is 27% of the critical value.
I. The mass density of all matter is 73% of the critical value.
J. The mass density of all matter is 100% of the critical value.

Answer 1

1.

A. Primordial Nucleosynthesis is said to have taken place in the time interval of 10 seconds to 20 mins after the Big Bang. So, this statement is false.

B. At low temperatures, the formation of the elements began to take place. Then ultimately forming up Helium. This statement is true.

C. When temperature fell below 3*10^8 K , the particles had insufficient energy to to undergo any more reactions. This statement is true.

D. Primordial Nucleosynthesis ended about 20 minutes or near about after the Big Bang. So, this statement is False.

Only statements B and C are true.

2. The abundance of primordial deuterium constitutes about mass density of normal matter about 23 percent and all matter about 4 percent of the total value. Hence, B and F are true.