Final answer:
Plasma began to form a few hundred thousand years after the Big Bang when the temperature of the universe dropped to 3000 K, allowing hydrogen and helium atoms to form and the universe to become transparent.
Step-by-step explanation:
Formation of Plasma in the Early Universe,Plasma began to form in the early universe not immediately after the Big Bang, but after a significant amount of time had passed, allowing the universe to cool sufficiently. This period is estimated to be a few hundred thousand years after the Big Bang, when the temperature dropped to approximately 3000 K.
At that juncture, the density of atomic nuclei was about 1000 per cubic centimeter - the conditions were ripe for electrons and nuclei to combine, forming stable atoms of hydrogen and helium. With the disappearance of free electrons to scatter photons, the universe turned transparent, allowing electromagnetic radiation to travel freely. This transition marked the decoupling of matter and radiation, each evolving separately henceforth. Prior to this point, the early universe remained hot enough for fusion, creating the lightest elements, but it was only after plasma formed that the universe became clear and the path was set for the formation of the heavier elements inside stars.