What elements primarily constituted the universe following Big Bang Nucleosynthesis (BBN)?

Answer

Hydrogen and helium-4.

Big Bang Nucleosynthesis, taking place roughly between 2 minutes and 20 minutes after the Big Bang, produced the universe's initial elemental composition, which was predominantly hydrogen and helium-4, with trace amounts of deuterium and lithium-7.

What elements primarily constituted the universe following Big Bang Nucleosynthesis (BBN)?

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