The correct option is 2 and 3 only.
Explanation
The Big Bang Theory explains the origin and evolution of the universe from a singular point of infinite density and temperature. As the universe expanded, it cooled, leading to the formation of matter and energy in various forms over distinct chronological stages.
Statement-wise Analysis:
- Statement 1 is Incorrect. The universe did not become transparent immediately after the Big Bang. For the first few hundred thousand years, the universe was extremely hot and dense, existing as an opaque plasma of ionized particles (protons, electrons, and photons). Light could not travel freely because photons were constantly scattered by free electrons. Transparency occurred only after the "Recombination" epoch.
- Statement 2 is Correct. The formation of the first neutral atoms occurred within approximately 300,000 years of the Big Bang. This event is known as recombination, where electrons combined with protons to form neutral hydrogen atoms.
- Statement 3 is Correct. During the recombination epoch (within 300,000 years), the temperature of the universe dropped to approximately 4,500 K. This cooling allowed atomic matter to form, and as free electrons were bound into atoms, the universe became transparent to radiation.
Key Takeaway:
The universe became transparent only after temperatures dropped sufficiently (around 4,500 K) to allow the formation of atomic matter, which occurred roughly 300,000 years after the Big Bang, not immediately.