How did the density of gas in the universe affect light travel before 380,000 years after the Big Bang?

Before 380,000 years after the Big Bang, the universe was in a state known as the "hot, dense plasma phase." During this epoch, the density of gas and matter was extremely high, and the temperature was also significantly elevated, causing the majority of hydrogen and helium atoms to exist in an ionized state. This ionization created a "fog" of charged particles, mainly electrons, which scattered and absorbed photons, effectively preventing light from traveling freely through space.

As a result, the universe was opaque during this period. It wasn’t until around 380,000 years after the Big Bang, when the universe cooled sufficiently for protons and electrons to combine into neutral hydrogen atoms, that the cosmos became transparent. This event is known as recombination, and it allowed light to travel freely across the universe, leading to the release of the Cosmic Microwave Background Radiation that we observe today.

The other options pertain to different conditions or interpretations that do not accurately capture the physical state of the universe during this critical early time.